Plant taxonomy is the branch of botany concerned with recognising, describing, identifying, naming and classifying plants. It provides an organised framework through which plant diversity can be studied and communicated.

1.1 Taxonomy and systematics

Taxonomy focuses strongly on identification, nomenclature and classification, while systematics embraces the study of diversity and relationships. In modern botany the two fields overlap extensively.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.2 Identification

Identification assigns an unknown plant to a known taxon by comparison with descriptions, keys, illustrations or authenticated specimens.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.3 Nomenclature

Nomenclature governs the scientific names applied to taxa. It provides rules so botanists can communicate about plants with reduced ambiguity.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.4 Classification

Classification arranges taxa into an ordered hierarchy according to stated principles and evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.5 Description

A taxonomic description records diagnostic and general characters in standard botanical language.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.6 Significance to biodiversity

Plant inventories, conservation assessments and vegetation studies depend on reliable identification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.7 Significance to agriculture

Correct names are essential when distinguishing crops, weeds, wild relatives, pests' host plants and useful germplasm.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

1.8 Significance to medicine

Accurate plant identification is critical where species are investigated or used as medicinal materials.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Taxonomic decisions are hypotheses based on evidence. Good taxonomy therefore requires clear characters, representative specimens, reproducible observations and appropriate nomenclatural practice.

2.1 Taxon

A taxon is a named or recognised group of organisms at any rank, such as a species, genus or family.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.2 Category and rank

Species, genus, family and order are ranks or categories. A particular named species or family is a taxon occupying a rank.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.3 Character

A character is an observable or measurable feature used in comparison; a character state is the particular expression of that feature.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.4 Diagnostic characters

Diagnostic characters distinguish a taxon from related taxa and are especially important in keys and descriptions.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.5 Homology

Homologous structures share evolutionary origin. Taxonomic comparison should avoid treating superficially similar but non-homologous structures as equivalent evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.6 Variation

Taxonomists must recognise variation caused by age, environment, geography, season and genetics.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.7 Circumscription

Circumscription defines what organisms are included within a taxon.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

2.8 Taxonomic revision

A revision re-evaluates a group using available specimens, literature and evidence and may alter species boundaries or classification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Hierarchical classification organises plants into nested taxa. The precise higher-level framework can change with systematic evidence, so students should understand both ranks and the characters used to recognise major plant groups.

3.1 Species

Species is the fundamental rank at which a binomial scientific name is applied.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.2 Genus

A genus groups one or more species regarded as closely related.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.3 Family

A family contains related genera and is a major practical level in flowering-plant identification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.4 Order

Orders contain related families and occupy a broader hierarchical level.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.5 Class and broader ranks

Classes and other higher categories organise major lineages. Their exact circumscriptions can change with phylogenetic research.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.6 Bryophyte-grade plants

Non-vascular land plants differ from vascular plants in organisation and life-cycle features and illustrate major divisions of plant diversity.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.7 Seedless vascular plants

Ferns and allies possess vascular tissues but reproduce through spores rather than seeds.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.8 Seed plants

Gymnosperms and angiosperms reproduce through seeds, while angiosperms are distinguished by flowers and enclosed ovules.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

3.9 Flowering-plant groups

Flowering plants include major lineages commonly recognised through combinations of embryological, vegetative, floral and molecular characters.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Artificial systems classify plants using a limited number of convenient characters. They can be efficient for identification but do not necessarily express overall natural or evolutionary relationships.

4.1 Purpose

An artificial system provides a manageable route for arranging or identifying plants.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.2 Selected characters

A small set of conspicuous characters may dominate the grouping.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.3 Advantages

Such systems can be simple, rapid and practical when the aim is identification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.4 Limitations

Unrelated plants may share the chosen character and be placed together, while related plants differing in that character may be separated.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.5 Sexual system as an historical example

Historical classifications based heavily on numbers or arrangements of reproductive structures demonstrate the power and limitation of restricted character sets.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.6 Artificial keys

A practical identification key can be artificial without being scientifically useless; its goal is often determination rather than phylogenetic reconstruction.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.7 Character reliability

Even artificial classifications require characters that are observable and consistently defined.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

4.8 Modern relevance

Artificial arrangements survive in practical tools where ease of identification is more important than expressing ancestry.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Natural systems attempt to use many characters so that groups reflect broad overall affinities rather than one or two selected features.

5.1 Overall resemblance

Vegetative and reproductive characters are considered together to recognise groups sharing numerous features.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.2 Multiple evidence

Natural classification reduces dependence on one potentially misleading character.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.3 Predictive value

Placement in a natural group can suggest additional features likely to occur in a plant.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.4 Reproductive characters

Flowers and fruits have historically been important because many reproductive structures are relatively informative taxonomically.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.5 Vegetative characters

Leaves, stems, roots and habit remain important, particularly when reproductive structures are unavailable.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.6 Limitations

Overall resemblance can still be affected by convergence and subjective character weighting.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.7 Historical importance

Natural systems represented an important transition from convenience-based arrangements toward biologically meaningful classification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

5.8 Relationship to phylogeny

Natural affinity can correspond partly with evolutionary relationship, but phylogenetic classification explicitly focuses on ancestry.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Phylogenetic classification seeks to arrange plants according to evolutionary relationships and common ancestry.

6.1 Common ancestry

Taxa are interpreted as lineages connected through descent.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.2 Shared derived characters

Characters inherited from a recent common ancestor can help recognise evolutionary groups.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.3 Convergence

Similar environmental pressures can produce analogous traits in unrelated plants, so superficial resemblance must be evaluated critically.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.4 Morphological evidence

Morphology remains important because evolutionary hypotheses must be connected to observable organisms and specimens.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.5 Molecular evidence

DNA sequence evidence has transformed understanding of many plant relationships and can reveal relationships not obvious morphologically.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.6 Fossil evidence

Fossils provide temporal and morphological evidence relevant to the history of plant lineages.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.7 Changing classifications

A phylogenetic classification can change when stronger evidence alters a relationship hypothesis.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

6.8 Practical implication

Students should not assume that every traditional group has remained unchanged under modern phylogenetic evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

A taxonomic key guides identification through a sequence of character choices. The NUC curriculum requires students not only to use keys but to design and construct them.

7.1 Dichotomous key

A dichotomous key presents two contrasting alternatives at each step.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.2 Couplet

The paired alternatives form a couplet; each alternative is called a lead.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.3 Good characters

Characters should be observable, contrasting and reasonably stable in the material for which the key is designed.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.4 Parallel wording

The two leads should compare the same feature or logically equivalent alternatives.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.5 Avoiding vague terms

Words such as large, small or beautiful are poor unless objectively defined.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.6 Indented keys

Indented keys display subsequent choices beneath previous choices.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.7 Bracketed keys

Bracketed keys keep paired leads together and direct the user to another numbered couplet.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

7.8 Confirmation

A name reached through a key should be checked against a description or authenticated specimen.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Key construction becomes easier when plant characters are organised before couplets are written.

8.1 Define the taxon set

A key works only for the plants it was designed to distinguish.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.2 Prepare a matrix

List taxa in rows and discriminating characters in columns.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.3 Choose an initial split

A strong first character separates the taxa efficiently and can be observed reliably.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.4 Subdivide groups

Continue splitting each remaining group until a single taxon is reached.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.5 Use positive statements

Where possible, describe what is present rather than relying excessively on absence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.6 Avoid overlapping states

Ranges or descriptions in opposing leads should not overlap.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.7 Test independently

Another user should identify specimens without being told the intended route.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

8.8 Revise failed couplets

Repeated mistakes at one couplet indicate that its characters or wording require improvement.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Experimental taxonomy uses observations and experiments to test taxonomic boundaries and sources of variation rather than relying only on preserved morphology.

9.1 Population sampling

Multiple individuals reveal the range of variation within populations.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.2 Common-garden experiments

Growing plants from different populations under similar conditions can help distinguish inherited differences from environmental plasticity.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.3 Transplant experiments

Reciprocal or controlled transplantation can investigate environmental contributions to phenotype where scientifically appropriate.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.4 Crossing evidence

Compatibility and fertility can provide evidence about relationships among populations or taxa.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.5 Cytological evidence

Chromosome number and behaviour can reveal polyploidy, hybridisation and lineage differences.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.6 Chemical evidence

Metabolites and other chemical characters can support comparisons among taxa.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.7 Integration

Experimental evidence is strongest when interpreted with morphology, ecology and other independent information.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

9.8 Limitations

Experimental feasibility differs among long-lived plants, rare species and organisms that cannot readily be cultivated.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Cytotaxonomy uses cytological evidence, particularly chromosomes, to address taxonomic and systematic questions.

10.1 Chromosome number

Differences in chromosome number can distinguish taxa or reveal evolutionary events.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.2 Ploidy

Diploid, polyploid and aneuploid conditions can contribute to plant diversification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.3 Chromosome morphology

Size, centromere position and other karyotypic features can provide comparative evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.4 Karyotype

A karyotype summarises chromosome complement and morphology.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.5 Meiosis

Pairing and segregation patterns can reveal chromosome homology and hybrid behaviour.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.6 Polyploidy

Whole-genome duplication is especially significant in plant evolution and can create reproductive barriers.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.7 Hybridisation

Chromosome evidence can support interpretation of hybrid origin.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

10.8 Limitations

Identical chromosome numbers do not prove taxonomic identity; cytological data should be integrated with other evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Chemotaxonomy uses chemical constituents as taxonomic evidence. Plants synthesise numerous compounds whose distribution can characterise lineages at different taxonomic levels.

11.1 Primary metabolites

Compounds central to basic metabolism are widespread and may have limited discriminatory power at some taxonomic levels.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.2 Secondary metabolites

Alkaloids, terpenoids, phenolics and related compounds can show useful distribution patterns.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.3 Proteins and enzymes

Biochemical variation can provide comparative evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.4 Chemical profiles

Chromatographic or spectrometric patterns can be compared among samples.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.5 Standardisation

Plant age, tissue, season and environment can influence chemical composition and should be controlled or recorded.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.6 Taxonomic markers

A compound is useful only when its distribution is sufficiently consistent and correctly associated with authenticated taxa.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.7 Applications

Chemical evidence can support identification, classification and investigation of relationships.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

11.8 Limitations

Similar chemistry can evolve independently, and environmental effects can alter metabolite abundance.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Modern plant taxonomy draws on many evidence sources. No source should automatically be treated as decisive in every case.

12.1 Morphology

Habit, stems, leaves, flowers, fruits and seeds provide the most directly observable taxonomic characters.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.2 Anatomy

Internal tissues, stomata, trichomes, wood and vascular features can distinguish taxa.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.3 Embryology

Ovule, embryo and developmental characters can provide systematic evidence.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.4 Palynology

Pollen and spore morphology can be taxonomically informative.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.5 Cytology

Chromosome data reveal karyotypic differences and evolutionary processes.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.6 Chemistry

Metabolites and biochemical profiles can supplement morphological classification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.7 Ecology and geography

Habitat and distribution patterns can support interpretation of taxonomic variation.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

12.8 Molecular data

DNA evidence can test relationships and species boundaries when sampling and identification are reliable.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Taxonomic data analysis transforms observations into explicit comparisons. The analytical method should match the type of data and the biological question.

13.1 Character coding

Qualitative characters can be coded into defined states while quantitative characters retain measurements or are transformed according to justified rules.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.2 Data matrix

Taxa or specimens are arranged against characters to create a structured dataset.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.3 Similarity

Similarity coefficients summarise resemblance under a specified character set.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.4 Distance

Distance measures quantify dissimilarity; different measures make different assumptions.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.5 Cluster analysis

Clustering groups operational units according to selected similarity or distance criteria.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.6 Ordination

Ordination summarises multivariate patterns in fewer dimensions and can reveal gradients or groupings.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.7 Character weighting

Giving all characters equal numerical weight does not guarantee equal biological information because correlated characters can overrepresent one feature system.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

13.8 Interpretation

Analytical output supports a taxonomic argument but does not replace biological judgement, specimen verification and nomenclatural rules.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Binomial nomenclature assigns a two-part scientific name to a species, consisting of a generic name and a specific epithet.

14.1 Generic name

The genus begins with a capital letter.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.2 Specific epithet

The specific epithet begins with a lower-case letter and is not normally used alone as the complete species name.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.3 Typography

Genus and specific epithet are conventionally italicised in printed text.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.4 Abbreviation

After an unambiguous first mention, the genus may be abbreviated.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.5 Author citation

Botanical names can include author information according to nomenclatural convention; the author citation is not part of the two-word binomial.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.6 Universality

Scientific names reduce confusion caused by multiple vernacular names.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.7 Name versus plant

A name is governed by nomenclatural rules, whereas taxonomic circumscription concerns the biological group to which the name is applied.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

14.8 Correct usage

Students should verify spelling and accepted usage from reliable botanical references.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Botanical nomenclature is governed by an international code whose principles aim at clarity, universality and stability while accommodating taxonomic research.

15.1 Independent nomenclature

Botanical nomenclature has its own formal rules and should not be assumed identical to zoological nomenclature.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.2 Typification

Application of a name is linked to a nomenclatural type.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.3 Priority

Earlier legitimate names generally have precedence within the rules, subject to provisions designed to preserve stability.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.4 Effective publication

A new name must satisfy publication requirements of the governing code.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.5 Valid publication

Additional formal requirements must be satisfied for a name to be established under the code.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.6 Legitimacy

A formally published name can still conflict with rules that affect its legitimacy.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.7 Conservation

Some names can be conserved to avoid disruptive changes and promote stability.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

15.8 Taxonomy versus nomenclature

The code governs names; it does not decide whether a taxonomist should recognise one species or several.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Flowering-plant classification uses combinations of vegetative, reproductive, anatomical and increasingly molecular evidence.

16.1 Habit

Trees, shrubs, herbs, climbers and other growth forms provide useful descriptive information but can evolve repeatedly.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.2 Leaves

Arrangement, complexity, venation, stipules, margins and surface structures are important characters.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.3 Inflorescences

Arrangement of flowers on an axis can be diagnostic.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.4 Flowers

Symmetry, sexuality, merosity, fusion and insertion of floral organs provide major characters.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.5 Androecium

Number, arrangement, fusion and anther characters are taxonomically useful.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.6 Gynoecium

Carpel number, ovary position, placentation and style features are especially important.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.7 Fruits and seeds

Fruit type, dehiscence and seed features support identification and classification.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

16.8 Character combinations

Reliable classification depends on combinations of characters rather than a single convenient trait.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

A standard description moves systematically through vegetative and reproductive structures so important diagnostic information is not omitted.

17.1 Habit and habitat

Begin with growth form and relevant ecological setting.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.2 Root and stem

Describe root type where available and stem form, surface, branching and special modifications.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.3 Leaves

Record arrangement, attachment, complexity, shape, apex, base, margin, venation and indumentum.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.4 Inflorescence

Describe whether flowers are solitary or arranged in a recognised inflorescence type.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.5 Flower

Record sexuality, symmetry, merosity and insertion.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.6 Calyx and corolla

Describe number, fusion, aestivation and conspicuous modifications.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.7 Androecium

Record stamens, fusion, attachment and anther characteristics.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

17.8 Gynoecium, fruit and seed

Describe carpels, ovary, locules, placentation, style and stigma, then fruit and seed characters.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

A floral formula compresses important structural information about a flower into symbols, letters and numbers.

18.1 Purpose

The formula allows rapid comparison of floral organisation.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.2 Symmetry

Symbols or notation can indicate actinomorphic or zygomorphic symmetry.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.3 Sexuality

The formula can indicate bisexual or unisexual flowers.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.4 Calyx

K represents calyx or sepals; numbers indicate parts, while brackets or parentheses can indicate fusion depending on convention.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.5 Corolla

C represents petals and can similarly show number and fusion.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.6 Perianth

P may be used where sepals and petals are not differentiated into calyx and corolla.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.7 Androecium

A represents stamens and indicates number or multiplicity.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

18.8 Gynoecium

G represents the gynoecium, with notation used to communicate carpel number and ovary position according to the adopted convention.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

A floral diagram is a schematic representation of a flower viewed in transverse orientation, showing number, position, fusion and relationships of floral organs.

19.1 Orientation

The diagram should show the flower's orientation relative to the inflorescence axis and bract where relevant.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.2 Whorls

Sepals, petals, stamens and carpels are arranged in their relative positions.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.3 Fusion

Connation within a whorl should be represented clearly.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.4 Adnation

Attachment between different floral whorls can be indicated where important.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.5 Ovary

Position, locules and placentation can be represented schematically.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.6 Symmetry

The diagram should make radial or bilateral organisation apparent.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.7 Formula versus diagram

A formula is compact symbolic text; a diagram provides spatial information. They complement rather than replace each other.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

19.8 Construction

Accurate diagrams must be based on observed or reliably described floral structure, not decorative drawing.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

The NUC curriculum includes unconventional identification methods and polyclave identification, which permit more flexible character entry than a fixed dichotomous path.

20.1 Limitations of single-access keys

A user blocked by one missing character may be unable to proceed through a traditional key.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.2 Multi-access identification

A polyclave allows users to select available characters in varying order.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.3 Character cards and matrices

Historically, multi-access systems could use punched cards or tabular character systems.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.4 Progressive elimination

Each selected character eliminates incompatible taxa until a manageable candidate set remains.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.5 Advantages

Users can bypass unavailable characters and begin with features that are easiest to observe.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.6 Limitations

Incorrectly scored characters can eliminate the correct taxon, so character definitions remain critical.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.7 Confirmation

Candidate names must still be checked against descriptions and specimens.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

20.8 Educational value

Polyclaves demonstrate that identification is a process of matching combinations of evidence rather than memorising one route.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Computerised identification implements taxonomic databases, interactive keys and character matrices electronically.

21.1 Interactive keys

Software can permit characters to be entered in flexible order and dynamically reduce candidate taxa.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.2 Image support

Images can clarify botanical terminology and character states.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.3 Databases

Taxonomic names, descriptions, distributions and specimen records can be linked.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.4 Scoring uncertainty

Some systems permit unknown or uncertain character states rather than forcing a choice.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.5 Efficiency

Large taxon sets can be searched more rapidly than with printed linear keys.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.6 Data quality

A sophisticated interface cannot compensate for incorrect taxon names, poor character definitions or misidentified reference specimens.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.7 Updates

Digital systems can incorporate revisions more readily than static printed keys.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

21.8 Role of expertise

Computerised identification supports, but does not eliminate, botanical observation and taxonomic judgement.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Although the NUC outline names sources of taxonomic data broadly, herbarium practice is central to obtaining and verifying plant taxonomic evidence.

22.1 Voucher specimens

A voucher permanently documents the material on which an observation or study was based.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.2 Field notes

Features lost during drying, such as flower colour, scent, latex and habit, should be recorded before pressing.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.3 Pressing and drying

Specimens are arranged to expose diagnostic features and dried to limit decomposition.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.4 Labels

Collector, number, date, locality, habitat and identification connect the specimen to its scientific context.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.5 Determination

Names can be updated through later expert examination while preserving the specimen's history.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.6 Type material

Nomenclatural types have special importance in applying plant names.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.7 Reference comparison

Authenticated specimens allow unknown plants to be compared with known material.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

22.8 Research value

Herbaria support taxonomy, floristics, ecology, conservation, phenology and historical distribution studies.

In practical plant taxonomy, this concept should be evaluated from correctly documented specimens and, where necessary, more than one source of evidence. Students should distinguish the character actually observed from the taxonomic interpretation made from it.

Practical 1: Recognising Major Plant Groups

Aim: To distinguish major classes or broad groups of plants using observable characters. Examine supplied bryophyte, fern, gymnosperm and angiosperm materials or authenticated illustrations. Record vascular tissue status, dominant visible structures, spores or seeds, and presence or absence of flowers. The exercise should teach character combinations rather than a single-feature shortcut.

Practical 2: Taxonomic Hierarchy

For several correctly identified plants, record species, genus, family and other ranks required by the instructor. Distinguish the rank name from the taxon occupying it. Verify spelling rather than reconstructing names from memory.

Practical 3: Character Matrix

Select six flowering plants. Construct columns for leaf arrangement, leaf complexity, venation, flower symmetry, petal fusion, stamen number, ovary position and fruit type. Use explicit states. Mark unavailable data as unknown rather than absence.

Practical 4: Dichotomous Key Construction

Use the character matrix to split the six plants into contrasting groups. Continue until each terminal lead identifies one plant. Exchange keys between groups for blind testing. Record any couplet at which another user fails and revise it.

Practical 5: Cytotaxonomic Data

Using supplied chromosome preparations, photographs or published teaching data, compare chromosome number and basic karyotypic features. Explain which conclusions the evidence supports and which conclusions require additional morphology, crossing or molecular evidence.

Practical 6: Chemotaxonomic Comparison

Use an instructor-approved dataset or safe laboratory demonstration to compare chemical profiles among authenticated plant materials. Record tissue sampled and analytical conditions. Discuss how environmental and developmental differences could alter chemical expression.

Practical 7: Morphological Description

Describe an unknown flowering plant systematically from habit through vegetative structures, inflorescence, flower, fruit and seed. Avoid informal expressions where standard botanical terminology is available.

Practical 8: Floral Dissection

Examine a fresh or preserved flower. Determine symmetry, sexuality, sepal and petal number and fusion, stamens, carpel organisation and ovary position. Use a hand lens or dissecting microscope where appropriate. Record observations before consulting the known family description.

Practical 9: Floral Formula

Translate the observations from the dissected flower into a floral formula using the notation taught by the department. Every symbol should correspond to an observed or verified feature.

Practical 10: Floral Diagram

Construct a transverse schematic diagram showing the relative positions of floral whorls, fusion, ovary organisation, bract and mother axis where applicable. The diagram should represent structure, not artistic appearance.

Practical 11: Herbarium Identification

Use a regional flora or taxonomic key to identify a herbarium specimen. Record every couplet selected. Confirm the resulting name by comparison with a description and authenticated specimen where available.

Practical 12: Polyclave Exercise

Enter a set of plant characters into a multi-access matrix. Begin with the most reliable visible characters and progressively eliminate incompatible taxa. Repeat after deliberately marking one character unknown and compare the remaining candidates.

Practical 13: Computerized Identification

Use an approved interactive key or teaching database. Evaluate the quality of character descriptions, images, taxonomic coverage and final confirmation. Record whether the system permits unknown states and how an incorrect entry affects the candidate list.

Practical 14: Herbarium Voucher Preparation

Where collection is authorised, assign a field number, record locality and fresh characters, press and dry representative material, prepare a complete label and identify the specimen. Collection must comply with institutional and conservation requirements.

Binary Character Matrix

Simple Matching Similarity

Interpretation

The calculation does not prove that A and B are the same species or that they share exactly 80% evolutionary ancestry. It describes resemblance for the five coded characters. Taxonomic interpretation requires broader evidence.

Character Weighting

If ten leaf measurements and one floral character are entered with equal numerical weights, leaves collectively dominate the dataset. Equal variable weighting therefore does not necessarily mean equal biological representation. Correlated characters and repeated measurements must be considered.

Missing Data

If the fruit of Taxon C was not available, “fruit dry” should not automatically be coded 0. Zero would assert that the fruit is not dry; missing means the state was not observed. This distinction can alter similarity calculations.

Cluster Interpretation

A clustering method can arrange taxa according to calculated resemblance. The resulting phenetic pattern should be described as an outcome of the chosen data and method. It should not automatically be called a phylogenetic tree.

Habit

State whether the specimen is herbaceous or woody and whether it grows as a herb, shrub, tree or climber. Note annual or perennial habit only where evidence is available. Habit is useful but rarely sufficient for identification because similar growth forms occur in unrelated families.

Stem

Describe orientation, branching, surface, cross-sectional form and special features such as spines, tendrils, latex or modified storage structures where present. Distinguish a spine derived from an organ from a superficial prickle when the structure can be determined.

Leaf Attachment and Arrangement

Record alternate, opposite or whorled arrangement; petiolate or sessile attachment; presence of stipules; and whether the leaf is simple or compound. Locate the axillary bud to distinguish a whole leaf from a leaflet.

Leaf Blade

Describe shape, base, apex, margin, venation, texture and surface hairs. Use measurements when size is diagnostically important. Avoid relying on colour alone because drying and environmental conditions alter colour.

Inflorescence

Determine whether flowers are solitary or arranged on a common axis. Recognise basic racemose, cymose or specialised arrangements where the specimen supports the determination.

Flower Symmetry and Sexuality

Determine whether the flower is radially symmetric, bilaterally symmetric or irregular and whether it is bisexual or unisexual. Examine more than one flower when possible because damage can mimic missing organs.

Perianth

Record sepals and petals separately when differentiated, including number, fusion, aestivation and modifications. Where tepals occur, describe the undifferentiated perianth appropriately.

Androecium

Record number of stamens, arrangement, filament fusion, attachment to petals where present, anther attachment and dehiscence when these characters can be observed.

Gynoecium

Determine carpel number, fusion, ovary position, number of locules, placentation, style and stigma. A transverse section of the ovary can reveal locules and placentation more reliably than external observation.

Fruit and Seed

Fruit type, dehiscence, seed number and seed structures can be highly diagnostic. A flowering specimen without fruit may remain uncertain if fruit characters are required by the key.

Reading a Floral Formula

Read the formula from general floral attributes through successive whorls. Identify symmetry and sexuality, then perianth, androecium and gynoecium. Parentheses commonly indicate fusion of members within a whorl, while other notation may indicate adhesion or ovary position according to the convention used. Students should follow the notation adopted by their department consistently.

From Flower to Formula

Do not memorise a formula and force a specimen to fit it. Dissect the flower, count organs, inspect fusion and section the ovary. The formula is a compressed report of those observations.

From Formula to Diagram

A formula provides numbers and relationships but not every spatial detail. When constructing the diagram, place the mother axis and bract, arrange whorls concentrically, represent fusion and show the gynoecium in the centre. Maintain the actual orientation and symmetry.

Diagram Quality Checklist

Why the Systems Should Not Be Confused

An identification key can deliberately use artificial characters and still work extremely well. A phylogenetic classification asks a different question: how are lineages related through ancestry? Students should therefore judge a system by its stated purpose rather than assuming that one classification method must perform every function.

1. National Universities Commission. Core Curriculum and Minimum Academic Standards for the Nigerian University System: Sciences. BOT 301 Plant Taxonomy.
2. Stace, C. A. Plant Taxonomy and Biosystematics.
3. Stuessy, T. F. Plant Taxonomy: The Systematic Evaluation of Comparative Data.
4. Judd, W. S. et al. Plant Systematics: A Phylogenetic Approach.
5. Simpson, M. G. Plant Systematics.
6. Radford, A. E. et al. Vascular Plant Systematics.
7. Current international botanical nomenclatural rules should be consulted for formal nomenclatural practice.

Case Study 1: Environmental Plasticity or Taxonomic Difference?

Two populations of the same provisional plant taxon occur in contrasting habitats. Plants in an exposed site are short with small thick leaves, while plants in a shaded moist site are taller with broader leaves. A weak taxonomic approach would immediately name two species from appearance alone. A stronger investigation first samples many individuals from both populations, records the full range of variation and searches for additional characters. Seeds or propagules can be grown under comparable conditions where feasible. If the morphological differences diminish under a common environment, phenotypic plasticity becomes a plausible explanation. If consistent inherited differences remain and are supported by reproductive, cytological, chemical or molecular evidence, taxonomic separation may deserve further investigation.

The central lesson is that morphology is evidence, but morphology must be interpreted in the context of variation. A taxonomist should ask whether a difference is discontinuous or continuous, whether intermediate individuals occur, whether it is associated with geography or ecology, and whether independent characters tell the same story.

Case Study 2: Polyploidy and Cytotaxonomy

Suppose a widespread plant has populations with one chromosome complement and another morphologically similar set with approximately twice the chromosome number. Chromosome doubling can alter cell size, fertility and reproductive compatibility. Cytological evidence therefore raises an important taxonomic hypothesis. Nevertheless, chromosome number alone does not automatically establish a new species. The investigator should compare morphology, geographical distribution, reproductive behaviour and other evidence. Where the polyploid population forms a stable lineage with consistent differences and reproductive separation, cytotaxonomy becomes a powerful component of the systematic interpretation.

Case Study 3: Chemical Profiles and Authenticated Material

Researchers compare leaf extracts from three supposed species and find that two share a distinctive chemical profile. Before interpreting this as taxonomic evidence, they must confirm specimen identity, tissue type, developmental stage, collection season and analytical conditions. If one sample was collected as young leaves during the rainy season and another as mature leaves in a dry period, chemical differences could reflect physiology rather than taxonomy. Voucher specimens allow later verification of every sampled plant.

Case Study 4: Conflicting Evidence

Morphology may group taxa A and B, while molecular evidence associates B more closely with C. The correct scientific response is not to hide the conflict. Researchers should examine sampling, character homology, possible hybridisation, incomplete lineage sorting, misidentification and analytical assumptions. Conflict can reveal biological history and can guide additional research.

Case Study 5: A Plant That Will Not Key

A student reaches a dichotomous-key couplet requiring fruit characters, but the specimen has flowers only. Choosing whichever lead “looks closer” is poor practice. The student should report the level to which the plant can be identified confidently, obtain fruiting material if possible, or compare authenticated specimens and additional references. Scientific uncertainty is preferable to a false species name.

Case Study 6: Old Herbarium Name

An herbarium sheet bears a name assigned forty years ago. A recent revision transfers the species to another genus. The old determination remains part of the specimen's history; a new annotation records the revised name rather than destroying the original label. This practice illustrates the difference between a physical voucher, a taxonomic determination and nomenclatural history.

Case Study 7: Artificial Key and Natural Classification

A key to local trees begins by separating plants with milky latex from those without it. Latex may be an efficient field character even when it does not define the deepest evolutionary division among the included families. The key remains useful because identification and phylogenetic classification have different immediate purposes. Students should therefore avoid criticising a practical key merely because its first split is not an evolutionary branching event.

Case Study 8: Digital Identification Error

An interactive key asks whether leaves are simple or compound. A student mistakes a leaflet for a simple leaf and enters the wrong state. The software efficiently eliminates the correct species. This demonstrates that computerised identification magnifies the value of good character observation; software cannot rescue incorrectly scored morphology. A useful digital system should allow the user to revise character states and preferably indicate which characters most effectively separate the remaining candidates.

Root Characters

Root systems can be taxonomically useful but are often missing from herbarium collections. Tap roots, fibrous systems, storage roots, pneumatophores and other modifications should be recorded when reliably observed. Absence from a pressed specimen is not evidence that the living plant lacks the structure.

Stem Characters

Stem cross section, branching, nodes, internodes, lenticels, surface hairs, wings, spines and underground modifications can support identification. Woody stems can also provide bark and anatomical characters. Developmental stage matters because young and mature stems may differ greatly.

Leaf Architecture

Leaf architecture includes arrangement, petiole, stipules, blade shape, venation and marginal pattern. Compound leaves require special care: a leaflet lacks the axillary bud that marks the base of a complete leaf. Misidentifying leaflets is a common source of errors in keys.

Indumentum

Plant hairs can be simple, branched, glandular or otherwise specialised. Density and structure may be diagnostic, but magnification is sometimes required. Because hairs can be lost from old specimens, the condition and age of material should be considered.

Inflorescence Architecture

Racemes, spikes, panicles, umbels, heads and cymose arrangements describe relationships among flowers and axes. Inflorescences can become highly modified, so interpretation should identify branching and flower position rather than relying only on overall silhouette.

Floral Symmetry

Actinomorphic flowers have multiple planes of radial symmetry, whereas zygomorphic flowers have bilateral organisation. Symmetry can be obscured if petals are damaged. Several flowers should therefore be examined before scoring the character.

Aestivation

The arrangement of sepals or petals in the floral bud can distinguish taxa. Valvate, twisted and imbricate relationships require examination before or during anthesis because fully opened flowers may make overlap difficult to determine.

Stamen Relationships

Stamens can be free or united by filaments or anthers and can be attached to other floral organs. Number alone is often less informative than the complete pattern of number, fusion, position and anther structure.

Placentation

Placentation describes the arrangement of ovules within the ovary. A careful transverse or longitudinal section can reveal axile, parietal, free-central, basal or other patterns. Students should relate the section to carpel organisation rather than memorising diagrams without specimens.

Fruit Characters

Fruits can be dry or fleshy, dehiscent or indehiscent, simple, aggregate or multiple according to developmental origin. Correct interpretation depends on the flower from which the fruit developed. Similar-looking mature structures can have different developmental origins.

Seed Characters

Seed number, size, surface, appendages and internal features can supplement other evidence. Seed morphology is particularly valuable when vegetative structures are reduced or convergent, but it should still be interpreted in combination with other characters.

Problem 1: Rank or Taxon?

Problem 2: Key Construction

Problem 3: Similarity

Problem 4: Cytotaxonomic Interpretation

Problem 5: Chemotaxonomic Control

Problem 6: Botanical Name Formatting

Problem 7: Formula versus Diagram

Problem 8: Polyclave Identification