Self-Fertilization in Amphicarpum purshii: Its Influence on Fitness and Variation of Progeny from Aerial Panicles

The annual grass, Amphicarpum purshii, grows in disturbed areas of the New Jersey Pine Barrens where it produces seeds both above and below ground. The cleistogamous subterranean spikelets do not open and never outcross; however, outcrossing is possible in aerial spikelets via chasmogamy. We investigated selffertilization of the aerial spikelets and its effects on seed set, germinability and variation of (maternal siblings) progeny by bagging aerial panicles as they emerged on 20 greenhouse-grown plants and making comparisons with 20 unbagged (open) controls. Aerial seed production and germinability did not differ between groups, but the percentage of aerial spikelets with seeds was significantly higher for open panicles. No fitness differences were detected for progeny from open or bagged panicles, but plants from seeds produced on open panicles were significantly taller and had a greater shoot and root biomass. Because these bulk analyses combined group and family effects, variance components were estimated to examine the influence of family origin on total variation. In 10 families, for all characters examined in plants from seeds of either bagged or open panicles, most (60 %) of the phenotypic variation was found within families, although significant family differences were detected for some traits. We concluded that a mixed breeding system which allows for some outcrossing coupled with high phenotypic plasticity explains the maintenance of considerable genotypic and phenotypic variation in this colonizing species.