Contrast in levels of morphological versus molecular divergence between closely related Eurasian species ofPlatanthera(Orchidaceae) suggests recent evolution with a strong allometric component

AbstractWe consider the conceptual relationship between pollinator specfificity, genetic isolation and species delimitation, critiquing Darwin’s (1877) hypothesis that differential placement of pollinia on the probosces and eyes of sphingid moths explained the divergence of the Eurasian orchids Platanthera bifolia and P. chlorantha — species that have similar geographic distributions, habitat preferences and flowering times. Subsequent workers have developed Darwin’s initial hypothesis into an oft-cited model system for co-evolutionary speciation via a prezygotic barrier. The four datasets gathered from the two species were: (a) morphometric data from 139 individuals of 21 populations in southern England, supported by SEM study of representative flowers; (b) spur-length measurements gathered by many fieldworkers from 3070 plants sampled across western Europe; (c) DNA sequences from two representative individuals of each species from nuclear ribosomal ITS and eight plastid regions; and (d) nrITS sequence d...