A Synopsis of Genera in Maloideae (Rosaceae)

The number of genera recognized in subfam. Maloideae by different authors has varied greatly; a historical summary is presented here. We have evaluated generic limits based on our own observations of a suite of morphological characters for about 200 species chosen to represent the taxonomic and geographic diversity of the approximately 940 species of Maloideae. A narrow circumscription of genera is generally adopted, with 28 genera recognized. Hesperomeles is considered distinct from Osteomeles; Eriolobus and Docyniopsis from Malus; and Aria, Chamaemespilus, Cormus, and Torminalis from Sorbus. Micromeles is included within Aria and Stranvaesia and Aronia within Photinia. The genera are either relatively small or relatively large: 19 genera have 11 or fewer species, seven between 26 and 97 species, and only two contain more than 100 species. The traditional division of Maloideae into two tribes is unwarranted and does not reflect relationships of the genera. The extensive hybridization between genera and subgeneric groups seems to reflect weak overall barriers to hybridization in the subfamily rather than indicate evolutionary relationships. Diagnoses are presented for each genus as well as a table comparing morphological characters for all genera. The following new combinations are made: Chamaemespilus alpina, Photinia floribunda, P. melanocarpa, P. pyrifolia, Malus subg. Sorbomalus, Torminalis clusii, and T. orientalis.