Evidence for pollination ecotypes in the yellow-fringed orchid, Platanthera ciliaris

Abstract

Platanthera ciliaris is a butterfly-pollinated, terrestrial orchid with a loose terminal raceme of 10-50 orange flowers, characterized by a long nectariferous spur. In the SE USA P. ciliaris occurs in the Appalachian mountains and coastal-plain physiographic provinces, but is found rarely in the intervening Piedmont. In the mountains, Papilio troilus (spicebush swallowtail) was the most frequent and effective visitor, whereas in the coastal plain, P. palamedes (palamedes swallowtail) was the predominant pollinator. Proboscis lengths of P. troilus (mean 23.3 mm) were significantly shorter than those of P. palamedes (28.7 mm). Floral characters, most notably spur length, also differed significantly between mountain (mean 23.8 mm) and coastal-plain (25.6 mm) plants. In 1983 and 1984, levels of pollinator service, as assessed by rates of removal and insertion of pollinia, were higher in the mountains (0.81 and 0.86) than in the coastal plain (0.63 and 0.67), and fruit-set was significantly greater in mountain (83.9% in 1983, 86.5% in 1984) than in coastal-plain (63.8% in 1983, 65.5% in 1984) populations. Selection pressure exerted through pollinator proboscis lengths has apparently resulted in pollination ecotypes of P. ciliaris. -from Author