Relationships of the Purple-Fringed Orchids Platanthera psycodes and P. grandiflora

Stoutamire, Warren

ABSTRACT: The vegetative and floral differences between two frequently confused species are discussed in terms of function. Platanthera psycodes is a widespread species with flowers adapted to visits by short-tongued lepidoptera, especially skippers of the genus Polites; the pollinaria are attached to the base of the proboscis. Platanthera grandiflora is a geographically more limited species with flowers adapted to visits by longer-tongued lepidoptera; the pollinaria are probably attached to compound eyes. The species overlap geographically and phenologically. Chromosome numbers are 2n = 42 in each species. Cultivated plants of each are partially self-incompatible but produce apparently normal embryos when intercrossed. Mechanical, seasonal, ethological, and distributional differences isolate the species. Habenaria and Platanthera are considered distinct but closely related genera. Platanthera psycodes is based upon a type at L, P. grandiflora on a type at AMES. Platanthera grandiflora and P. psycodes have affinities with three other eastern North American species characterized by tri-partite, fringed, or erose labella. Species pairs within this group, based on column structure, include grandiflora-peramoena and psycodes-lacera. The column of P. leucophaea is morphologically intermediate in form.