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Sorbus subgenus Sorbus
Sorbus aucuparia - European Rowan
Sorbus americana - American Rowan
Sorbus cashmiriana - Kashmir Rowan
Sorbus commixta - Japanese Rowan
Sorbus decora - Showy Rowan
Sorbus esserteauiana - Esserteau’s Rowan
Sorbus glabrescens - White-fruited Rowan
Sorbus harrowiana - Harrow Rowan
Sorbus hupehensis - Hubei Rowan
Sorbus maderensis - Madeira Rowan
Sorbus microphylla - Small-leaf Rowan
Sorbus oligodonta - Kite-leaf Rowan
Sorbus reducta - Dwarf Rowan
Sorbus rufopilosa - Tsema Rowan
Sorbus sargentiana - Sargent’s Rowan
Sorbus scalaris - Ladder Rowan
Sorbus sitchensis - Sitka Rowan
Sorbus vilmorinii - Vilmorin’s Rowan
Plus several other species
Sorbus subgenus Aria
The rowans are plants in the family Rosaceae, in the genus Sorbus, subgenus Sorbus. They are native throughout the cool temperate regions of the Northern Hemisphere, with the highest species diversity in the mountains of western China and the Himalaya, where numerous apomictic microspecies occur.
Rowans are mostly small deciduous trees 10-20 m tall, though a few are shrubs. The leaves are arranged alternately, and are pinnate, with (7-)11-35 leaflets; a terminal leaflet is always present. The flowers are borne in dense corymbs; each flower is creamy white, and 5-10 mm across with five petals. The fruit is a small pome 4-8 mm diameter, bright orange or red in most species, but pink, yellow or white in some Asian species. The fruit are soft and juicy, which makes them a very good food for birds, particularly waxwings and thrushes, which then distribute the rowan seeds in their droppings.
Rowan is used as a food plant by the larvae of some Lepidoptera species; see Lepidoptera that feed on Sorbus.
The best known species is the European Rowan Sorbus aucuparia, a small tree typically 4-12 m tall growing in a variety of habitats throughout northern Europe and in mountains in southern Europe and southwest Asia. Its berries are a favourite food for many birds and are a traditional wild-collected food in Britain and Scandinavia. It is one of the hardiest European trees, occurring to 71° north in Vardø in arctic Norway, and has also become widely naturalised in northern North America.
The greatest diversity of form as well as the largest number of species is in Asia, with very distinctive species such as Sargent’s Rowan Sorbus sargentiana with large leaves 20-35 cm long and 15-20 cm broad and very large corymbs with 200-500 flowers, and at the other extreme, Small-leaf Rowan Sorbus microphylla with leaves 8-12 cm long and 2.5-3 cm broad. While most are trees, the Dwarf Rowan Sorbus reducta is a low shrub to 50 cm tall. Several of the Asian species are widely cultivated as ornamental trees.
North American native rowans 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.
For other Sorbus species, see whitebeam (Sorbus subgenus Aria) and the genus article Sorbus. 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.).