Sorbus
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Sorbus, or the Whitebeams, Rowans, and Service Trees, is a genus of trees and shrubs in the subfamily Maloideae of the Rose family Rosaceae.
The genus is divided into two main and three or four small subgenera:
- Sorbus subgenus Sorbus, the rowans, with compound leaves usually hairless or thinly hairy below; fruit carpels not fused; type species Sorbus aucuparia (European Rowan or Mountain Ash). Distribution: cool-temperate Northern Hemisphere.
- Sorbus subgenus Aria, the whitebeams, with simple leaves usually strongly white-hairy below (hence the name, from German Weissbaum, 'white tree'); fruit carpels not fused; type species Sorbus aria (Common Whitebeam). Distribution: temperate Europe & Asia.
- Sorbus subgenus Micromeles, an indistinct group of a few east Asian species (e.g. Sorbus alnifolia, Korean Whitebeam) with narrow leaves; doubtfully distinct from and often included in subgenus Aria. Distribution: temperate northeast Asia.
- Sorbus subgenus Micromeles, an indistinct group of a few east Asian species (e.g. Sorbus alnifolia, Korean Whitebeam) with narrow leaves; doubtfully distinct from and often included in subgenus Aria. Distribution: temperate northeast Asia.
- Sorbus subgenus Cormus, with compound leaves similar to subgenus Sorbus, but with distinct fused carpels in the fruit; just one species, Sorbus domestica (True Service Tree). Distribution: warm-temperate Europe.
- Sorbus subgenus Torminaria, with rather maple-like lobed leaves with pointed lobes; fruit carpels not fused; just one species, Sorbus torminalis (Wild Service Tree). Distribution: temperate Europe.
- Sorbus subgenus Chamaemespilus, a single shrubby species Sorbus chamaemespilus with simple, glabrous leaves and pink flowers with erect sepals and petals. Distribution: mountains of southern Europe.
- Hybrids are common in the genus, including many between the subgenera; very often these hybrids are apomictic (self-fertile without pollination), so able to reproduce clonally from seed without any variation. This has led to a very large number of microspecies, particularly in western Europe (including Britain) and parts of China.