ABSTRACT
Mating systems range from species that are obligately outcrossing (e.g., dioecious or completely self-incompatible species) to species with mixed mating systems, to obligate selfers. In numerous species, mechanisms that facilitate selfi ng within a fl ower are delayed, thus providing a back-up method for reproduction if outcrossing fails (e.g., when pollinators are not suffi cient). For some of those species, selfi ng can be rare and occurs at increased rates only when outcrossing fails (e.g., Lloyd and Schoen 1992; Harder and Barrett 2006). The proportion of offspring produced via selfi ng versus outcrossing thus varies considerably across and within species.
