Rowan Several of the Asian species are widely cultivated as ornamental trees. North American native species in the subgenus "Sorbus (Sorbus)" include the American mountain-ash "Sorbus americana" and Showy mountain-ash "Sorbus decora" in the east and Sitka mountain-ash "Sorbus sitchensis" in the west. Numerous hybrids, mostly behaving as true species reproducing by apomixis, occur between rowans and whitebeams; these are variably intermediate between their parents but generally more resemble whitebeams and are usually grouped with them (q.v.). Rowans are excellent small ornamental trees for parks, gardens and wildlife areas. Several of the Chinese species, such as White-fruited rowan ("Sorbus glabrescens") are
Sorbus torminalis the bark on old trees. The species has sometimes been placed in its own genus, "Torminalis". Recent molecular phylogenetics confirms an earlier taxonomic opinion that the genus "Sorbus" as defined in the broad sense is not monophyletic, but the simple-leafed species traditionally included in "Sorbus" are a monophyletic group; this species would be included in a clade called "Aria" (genus "Aria" or "Sorbus" subgenus "Aria") as the species "Aria torminalis" Beck. It is a sexually reproducing diploid species that forms diploid and polyploid hybrids with members of subgenus "Aria" (whitebeams). A number of often very localised stable apomictic polyploid species