Why is population information crucial for taxonomy?

Despite acceptance in the scientific community that population information and suites of characters are crucial for circumscription of taxonomic groups, new taxa continue to be published on the basis of few herbarium specimens. Given that there is increasing evidence that hybridisation plays an integral part in evolution, it is desirable to identify groups in which it occurs.

Corolla characters assessed.
Corolla characters assessed. Nectar pouches and corolla colour: (A) ‘deep-red’ corolla, one ‘dominant’ nectar pouch—the main nectar pouch in the middle is distinctly larger, and has a different colour; (B) ‘deep-red’ corolla, ‘different’ nectar pouches—the middle nectar pouch is perceptibly larger, and the pouches next to the main one are larger then the others, and all are distinctly coloured; (C) ‘pink’ corolla, ‘different’ nectar pouches; (D) ‘cream’ corolla, ‘equal’ nectar pouches—no distinct colouring, and all are the same size. ‘pink-red’ corolla colour is not shown, as it was indistinguishable from ‘deep-red’ in photographs. (E) Typical R. irroratum corolla; (F) typical R. delavayi corolla, shown are measurements of ‘corolla length’—measured as the length from the calyx to the tip of the main petal (compare A, middle petal), and ‘corolla width’—measured at the top of the corolla tube (where the petals are just still all fused). Maculation: (G) ‘none’—absolutely no markings visible; (H, I) ‘scarce’—some light spots visible on fewer than three petals; (J) ‘few’—spots clearly visible on three petals; (K, L) ‘many’—spots clearly visible on all petals.

In a recent study published in AoB PLANTS, Marczewski et al. showcase how population variation can be used to identify distinguishing characters and why closely related species that are growing in sympatry should be considered when describing new taxonomic entities.

Reference

Marczewski, T., Ma, Y.-P., Zhang, X.-M., Sun, W.-B., & Marczewski, A. J. (2016). Why is population information crucial for taxonomy? A case study involving a hybrid swarm and related varieties. AoB Plants, 8, plw070. http://dx.doi.org/10.1093/aobpla/plw070