Floral morphology and late-acting self-incompatibility in Apocynum cannabinum (Apocynaceae)

Scanning electron and fluorescence microscopy were used to clarify some asp ects of the floral morphology of Apocynum cannbinum. Insects are required f or pollination, since the floral morphology prevents autogamy and minimizes intrafloral self-pollination. Flowers hand-pollinated with self-pollen nev er set fruit, but 10.6% of cross pollinations produced fruit. Self-pollen d id germinate,, however, and produced abundant tubes that grew through the p istil and entered the ovule micropyles. The proportion of ovules penetrated by self- and outcross-pollen tubes was not statistically significantly dif ferent. These results suggest that A. cannabium possesses late-acting self- incompatibility, similar to that in the closely related Asclepiadaceae.