Uncorrelated variation in widespread species: Species delimitation in Strobilanthes echinata Nees (Acanthaceae)

Species that show high levels of infraspecific variation in several quantitative characters are often difficult to accommodate adequately in taxonomies. The recognition of a large number of formal taxa, at either specific or infraspecific rank, may suggest incorrectly that the variation is discrete and discontinuous. However, the alternative of recognizing a smaller number of variable taxa is resisted by some because this may conceal localized patterns of variation. The problem is particularly acute for taxa that occur over a large geographical area, because specimens taken from widely separated localities may appear very distinct when considered without reference to the full range of variation. The difficulty in delimiting Strobilanthes echinata Nees (Acanthaceae) highlights the problems taxonomists face in dealing with such widespread and variable taxa. This species has the characteristics of an ochlospecies, with multiple characters varying in an uncorrelated fashion across a wide geographical area. We recognize a single, widespread, and morphologically variable species, and reduce a large number of names to synonymy. We explain why we do not recognize formal infraspecific taxa and provide a detailed description of the variation seen in both vegetative and reproductive characters. © 2008 The Linnean Society of London.