Plant Taxonomy and Systematics: Names, Ranks and Evidence
The backbone of nomenclature
Systematics questions reward command of the International Code of Nomenclature. Know that a species name is a binomial, always italicised, with the genus capitalised and the specific epithet lower case; the author citation follows in roman type. Understand valid publication, effective publication, the principle of priority, type specimens (holotype, isotype, lectotype, neotype) and the rule that a new combination requires a basionym. Learn rank endings: -aceae for families, -ales for orders, -phyta for divisions, and the -eae ending for tribes.
Classification systems and evidence
Be able to outline the progression from artificial to natural to phylogenetic systems, and the contributions of Bentham and Hooker, Engler and Prantl, Hutchinson, Cronquist and the Angiosperm Phylogeny Group. Understand cladistics: monophyly, paraphyly and polyphyly, homology versus analogy, and the use of synapomorphies. Appreciate that molecular data (rbcL, matK, ITS) reshaped families, and that APG places monocots and eudicots in a nested framework.
Traps to expect
Examiners love to test whether a group is monophyletic; for example, dicotyledons are paraphyletic, and so are many traditional families. Another trap is confusing a taxonomic character with a taxonomic rank, or treating a variety as a species. Watch for questions on type method and on the difference between nomenclature and classification.
Rule of thumb
For any taxon, ask: Is it monophyletic? What synapomorphy defines it? What rank and ending apply? If a name change is proposed, check whether priority and the type method support it.
Worked example
A new species is described in a genus with an existing type. The author must designate a holotype, publish a Latin diagnosis or description, and cite the type locality; the name is valid only if these conditions are met.