Mating system
We coded species as selfing, mixed-mating, or outcrossing, as identified by the authors in each study. Selfing species included strictly autogamous species. They were rare (N=7) and not included in the final 337-species dataset, due to their low sample size. Mixed-mating species included those that undergo both outcrossing and selfing to some extent, through either autogamy or geitonogamy (Goodwillie, Kalisz, & Eckert, 2005). Outcrossing species included plants that are self-incompatible, unisexual (i.e. monoecious or dioecious), or dichogamous hermaphrodites; i.e. either having the male reproductive organs come to maturity before the female organs (protandry), or vice versa (protogyny).