Abstract

Differences in the areal extent of the geographic ranges of sister species are noteworthy. Possible explanations of these differences in particular cases help evaluate and interpret generalizations based on survey data or theory, and contribute to better understanding the biology of individual species. We document range, breeding system, morphology, niche breadth, and leaf vascular architecture in western North American hawthorns for which phylogenetic relationships and ploidy level are known. Species distribution data from herbarium specimens and online databases were analyzed in order to compare climate niches described by BIOCLIM variables. Flow cytometry documented ploidy level and breeding system. Voucher specimens provided morphometric data that were analyzed using uni- and multivariate methods. Black-fruited members of Crataegus subg. Sanguineae of western North America previously identified as hybrids are presumptively self-fertile tetraploids with pseudogamous gametophytic apomixis; their morphologies, geographic ranges, and niche characteristics resemble those of their diploid, sexual parent or are intermediate between them and those of their other parent, one or both of two partially sympatric tetraploid apomicts in red-fruited C. subg. Americanae with much wider distributions. Geographic parthenogenesis (larger range sizes in apomicts, compared to sexuals) may have less to do with adaptation than it does with reproductive assurance in the pseudogamously apomictic and self-compatible hybrids. Wider climatic niche breadth in allopolyploids compared to diploid similarly may be more due to parental traits than to effects of genome duplication per se.