What is Suksdorf’s hawthorn? Revision of the Western North American 20-stamen black-fruited hawthorns (Crataegus series Douglasianae, Rosaceae subtribe Malinae)

An agamic complex of 20- and 10-stamen, black-fruited hawthorns (Crataegus subg. Sanguineae, sect. Douglasianae) occurs in western North America, with a 10-stamen taxon disjunct the upper Great Lakes basin. Here, we recircumscribe 20-stamen taxa at core this (C. ser. Douglasianae). This is needed order to distinguish between presumptively ancestral diploid its allo- autopolyploid derivatives, all differing breeding system, distribution, morphology, pattern genetic variation. The earliest name for these taxa, Crataegus gaylussacia A. Heller, was given distinctive plants Marin Sonoma counties California that have recently been shown be autotriploids. In Flora however, applied 20-stamen, hawthorns. We C. gaylussacia, also typify slightly younger name, suksdorfii (Sarg.) Kruschke, specimen from southern Washington diminished pollen fertility found allopolyploid, apomictic occurring east Cascades, northern north southernmost Alaska. Finally, recognize diploid, self-incompatible, sexual west Cascades southwestern as rhodamae-loveae sp. nov. Together predominantly tetraploid, apomictic, self-fertile douglasii Lindl. segregates (discussed detail companion paper), species are linked by whole genome duplications associated most cases hybridization, members red-fruited Americanae, each other. suggest provides model understanding other such groups related resulting fertilization unreduced gametes (facilitated but not necessarily dependent on occurrence gametophytic apomixis), often together hybridization. note an earlier effort DNA barcoding hawthorn provided limited support our taxonomic decisions here demonstrated some utility original plant loci like Crataegus. advocate will warrant consideration when revised light data those employed here.