The life and death of a mythical British endemic,Orchis militarisL. var.tenuifronsP.D. Sell: why infraspecific taxonomy requires a field-based morphometric approach

Detailed morphometric comparison of the three extant English populations of Orchis militaris with a population from the Vercors region of southern France uses both univariate and multivariate approaches. These analyses reveal only subtle distinctions of similar magnitude between the four populations, and slightly greater variation within the French population than its English equivalents. Morphology does not offer strong support to molecular evidence that the Suffolk population became established only recently. Of the seven morphological characters (six vegetative) previously advanced as diagnosing O. militaris var. tenuifrons P.D. Sell — a taxon endemic to the Chiltern Hills and supposedly distinct from Suffolk and Continental populations — none is in fact diagnostic. Although other characters, notably rosette leaf number and labellum limb widths, offer better discrimination, the populations in Buckinghamshire and Oxfordshire are better perceived as merely representing the subtle morphological differences that are evident among most conspecific populations of allogamous angiosperms. More generally, vegetative features are shown to exhibit two to three times the size variance of floral features. We argue that infraspecific taxa have a continued role to play in systematic biology, but that effective, predictive taxonomy requires thorough field-based observation and sampling linked to quantification through both morphometric and molecular approaches.