Population Structure and Reproductive Ecology in the Maloideae (Rosaceae)

The available data suggest that the population structure of maloid species may be affected dramatically by features of their breeding system, and by their reproductive ecology in general. Morphometric data from Amelanchier, Crataegus, and Sorbus demonstrate associations be- tween the occurrence of uniparental reproduction (apomixis and selfing) and polyploidy with topodeme phenotypic variability. These associations appear to be modified by factors such as fe- cundity, propagule size, and differences in shade tolerance between and within genera. Uniparental reproduction, abundant seed production, and the short time available in which to colonize recently disturbed sites decrease the number of genotypes in maloid topodemes. At present, however, genetic data with which to test this assertion are lacking. Rigorous evaluation is necessary in view of the possibility that much of the taxonomic complexity of genera such as Amelanchier, Crataegus, and Sorbus is due at least in part to naive assumptions about population structure in these genera on the part of earlier taxonomists. Their ignorance of the roles played by hybridization, uniparental reproduction, and polyploidy may have led them to recognize as species individual genotypes.