A phylogeny of Photinia sensu lato (Rosaceae) and related genera based on nrITS and cpDNA analysis

Photinia Lindl. sensu lato including Photinia, Pourthiaea, Stranvaesia and Aronia, occurs primarily in eastern and southeastern Asia, eastern North America, and Central America. However, generic circumscription within the group has been a taxonomic problem. Phylogenetic analyses were conducted in Photinia sensu lato and several related genera based on two chloroplast DNA regions and nrITS sequences, separately and in combination, and nine non-molecular characters were plotted onto a phylogeny based on the combined molecular data. All phylogenetic trees produced indicated that Stranvaesia should be merged into Photinia, while Pourthiaea and Aronia should be delimited as two separate genera. Ph. davidsoniae and Ph. nussia form a separate clade in our consensus trees and Ph. davidsoniae is speculated to have originated from hybridization between Photinia and some other genus of Pyrinae characterized by spines on the stem, but the specific hybrid origin cannot be inferred in detail due to lack of samples included in our data. The relationships among two taxa of Photinia from Mexico and Central America and species distributed in eastern Asia are also discussed. Ph. microcarpa subsp. hintonii var. hintonii is sister to species in eastern Asia is supported, but with weak support, while the position of a second taxon from Mexico, whose identity is uncertain, is unresolved, indicating the need for further taxonomic and biogeographic studies of these species. Incongruence between chloroplast and nuclear data supports the hypothesis of a hybrid origin of the monospecific genus Heteromeles, with a recent ancestor of extant Photinia as the probable male parent.