Pollination systems in the Asclepiadaceae: a survey and preliminary analysis

Using published and unpublished records of pollination in the dicot family Asclepiadaceae (the ‘milkweeds’) we offer a preliminary analysis of present-day pollination systems in the family. Variation in principal pollinators is apparent at and below the tribal level. The tribes Marsdenieae and Stapelieae and Asclepiadeae subtribe Gonolobineae are primarily Diptera-pollinated, a tentative conclusion also for the tribe Periploceae, and we emphasize the ubiquity and importance of fly pollination in the family. The rest of the tribe Asclepiadeae is pollinated in the main by Hymenoptera and Lepidoptera. Lack of data makes it impossible to draw even initial conclusions for the remaining tribes, Secamoneae and Fockeeae. Within the Asclepiadeae, there has been a trend towards more diverse pollination systems (incorporating butterflies and wasps) in the New World compared to the Old World. In terms of the taxonomic breadth of pollinators of individual species, Stapelieae is the most specialized tribe. We emphasize that this is only a preliminary account of pollination in the Asclepiadaceae, and detail areas where further work is urgently required.