Mating systems directly control the transmission of genes across generations, and understanding the diversity and distribution of mating systems is central to understanding the evolution of any group of organisms. This basic idea has been the motivation for many studies that have explored the relationships between plant mating systems and other biological and/or ecological phenomena, including a variety of floral and environmental characteristics, conspecific and pollinator densities, growth form, parity, and genetic architecture. In addition to these examples, a potentially important but poorly understood association is the relationship between plant mating systems and genome duplication, i.e., polyploidy. It is widely held that polyploid plants self-fertilize more than their diploid relatives, yet a formal analysis of this pattern does not exist. Data from 235 species of flowering plants were used to analyze the association between self-fertilization and ploidy. Phylogenetically independent contrasts and cross-species analyses both lend support to the hypothesis that polyploids self-fertilize more than diploids. Because polyploidy and self-fertilization are so common among angiosperms, these results contribute not only to our understanding of the relationship between mating systems and polyploidy in particular, but more generally, to our understanding of the evolution of flowering plants.

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Summary 1.We examined the fitness consequences of pollen limitation in the valley oak (Quercus lobata Ne´e, Fagaceae), a wind-pollinated, predominantly outcrossing tree endemic to California, by examining the relationship between within-year phenology and acorn production over an 8 year period. 2. We predicted that pollen limitation should result in trees flowering relatively early and late in the season, when fewer trees are in flower, to experience reduced reproductive success compared to trees flowering during the middle of the season. 3. Despite considerable variation in acorn production from year to year, analyses confirmed this prediction and indicated that there was significant overall stabilizing selection on budburst date consistent with the pollen limitation hypothesis. 4. Analyses including herbivory and pre-budburst temperatures at individual trees revealed significant correlations with acorn production, but we still found significant stabilizing selection on budburst date even when considering these variables. 5. Synthesis. Pollen limitation, as indicated by stabilizing selection on within-year flowering phenology, significantly affects acorn production by individual trees in Q. lobata and has the potential to influence other key life-history features including masting behaviour and spatial synchrony.