Flowering Phenology and Seed Set in Claytonia virginica (Portulacaceae)

SCHEMSKE, D. W. (Dept. Ecol., Ethol. and Evol., Vivarium Bldg., Univ. Ill., IL 61820). Flowering phenology and seed set in Claytonia virginica (Portulacaceae). Bull. Torrey Bot. Club 104: 254-263. 1977.-Data oll seed set anid floweriiig pheiiology were obtained for Claytonia virginica L. in Brownfield and Hart Woods in central Illinois. At both sites flowering time varied markedly between years with temperature as the proximate cue. Mean seed set per ovary at Brownfield and Hart was greatest in 1974, lowest in 1975 and intermediate in 1976. As determined from ceinsuses of flowers on marked inflorescences at Brownfield in 1975 and 1976, seed set was highest in flowers first-pistillate betweeln the 25 and 50% cumulative flowering poiints. In both years, flowers opening early and late in the phenological sequence had reduced seed production and seed set declined rapidly during the latter periods of heavy flowering. Maximum seed set coincided with the first of the two peaks in the bimodal 1975 flowering sequence but preceded peak flowering in 1976. Abortion rates were highest in flowers first-pistillate during the final periods of Claytonia flowering when reduction of light due to canopy development was most severe. The evolution of Claytonia flowering time has been influenced by 1) cold temperatures early in the season which milnimize pollination probabilities and 2) developmenit of the cainopy late in the season which reduces photosynthetic capabilities.