REPRODUCTIVE BIOLOGY OF THREE SPECIES OF EUPHORBIA SUBGENUS CHAMAESYCE (EUPHORBIACEAE)

The breeding system, pollen tube development, and floral biology of three species of Euphorbia subgenus Chamaesyce from southeastern Arizona have been examined in field and greenhouse studies. E. albomarginata is entirely dependent on insect vectors for pollination and seed production, E. capitellata requires insect visitors for maximum seed set but is capable of limited self-pollination, and E. hyssopifolia is self-pollinating and entirely independent of insect vectors. All three species are self-compatible. The differences in reliance on insect vectors, diversity of insects and probable amount of outcrossing are related to differences in cyathial size and arrangement. The reproductive biology of the three species is similar to that described for other weedy plant taxa.