Although flowering plants are famous for their diversity of life histories and reproductive systems, this diversity has considerable structure. Particular features ave evolved many times independently, in distantly related plants, and some features are much more common than others. For example, most species of flowering plants are hermaphroditic, with each individual capable of reproducing as both a male and a female parent. The other reasonably common sexual systems are dioecy (separate males + females) and gynodioecy (females + hermaphrodites). Why is hermaphroditism the most common system, and why are some systems (e.g., androdioecy: males + hermaphrodites) vanishingly rare? My students and I try to identify environmental factors that determine how natural selection shapes plant reproduction and life history, and to understand how genetics, physiology, and development limit evolutionary responses to selection. We apply an integrative approach that includes studies of resource-allocation theory, transmission genetics, population genetics, quantitative genetics, natural selection, geographic distribution and geographic variation, pollination biology, experimental population biology, and physiological ecology. Current projects include studies of reproductive systems and life history in the California wildflower Clarkia xantiana and studies of the population biology of the Iowa wildflowers Linum rigidum and L. sulcatum.