How do plants divide their effort between male and female reproduction? A well-developed theory predicts equal investment unless one sex is a better performer, that is, brings more fitness than the other for each unit of resource investment.
Petersen and Burd find that a primitive vascular plant genus, Selaginella, makes male-biased reproductive investments in 13 of 14 species examined. Flowering plants overwhelmingly direct their resources into the female investments of fruits and seeds. The female spores of Selaginella, however, may not disperse as well as the smaller male spores, giving male function the advantage that explains the sex allocation bias.