Most Malpighiaceae have bisexual flowers, but dioecy occurs in three clades. Spachea is an American genus with two types of apparently bisexual flowers borne on different plants: One has dehiscent anthers and a small gynoecium that does not set seeds; the other has indehiscent anthers and a large seed-producing gynoecium. The madagasikarioid clade contains three genera endemic to Madagascar, Madagasikaria, Microsteira, and Rhynchophora. At least some species in all three genera are morphologically androdioecious, some plants bearing wholly staminate flowers, others bearing flowers with both stamens and a gynoecium. Pollen produced by the "bisexual" flowers is inaperturate and probably serves only as fodder for pollinators, so these plants, like Spachea, seem to be functionally dioecious. In the Mexican genus Lasiocarpus at least two species are strictly dioecious, while at least two others are morphologically androdioecious -- the apparently bisexual flowers have a functional gynoecium and about one-third to one-half as many stamens as the staminate flowers. Pollen grains from staminate flowers are colporate, while those from "bisexual" flowers have ectoapertures (colpi) but lack endoapertures (pores), so they are probably also nongerminating fodder, making the "androdioecious" species functionally dioecious. The breeding systems in these three lineages have evolved independently, as shown by their distribution on the family-level phylogeny; in every case their closest sister clades have standard bisexuality. Lasiocarpus and the Malagasy genera flower during the dry season in very xeric vegetation and lack glands on the sepals. Pollen is probably the reward for pollinators, and similarities of the habitat or pollination biology may have resulted in the parallel evolution of dioecy in those two clades. However, Spachea grows in mesic environments and has the oil glands found in most neotropical Malpighiaceae; no obvious ecological or morphological peculiarities suggest why dioecy evolved in that genus.

Key words: breeding systems, dioecy, Malpighiaceae