Sorbus is a genus of trees and shrubs in the family Rosaceae, comprising 100-200 species. It is commonly known as whitebeam, rowan, service tree, and mountain ash. This genus contains some of the best ornamental trees for gardens, parks and wildlife area. The trees can tolerate pollution and also withstand wind.
The rowan or mountain ash are small trees or shrubs native to the cool temperate regions of Northern Hemisphere, with the highest species diversity in the mountains of western China and the Himalaya. Rowans, 10-20 m tall, are mostly small deciduous trees with alternate-arranged leaves, pinnate, and with 7-35 leaflets. A terminal leaflet is always present. In spring to early summer, creamy white five-petaled flowers are borne in dense corymbs. The soft and juicy fruit is a small pome 4-8mm in diameter, bright orange or red in most species, but pink, yellow or white in some Asian species. The fruits are a favorite for birds such as waxwings and thrushes. The birds helps to distribute the seeds in their droppings. Rowan is also food plant for larvae of some Lepidoptera (butterflies and moths) species including Mottled Beauty, Scalloped Oak, The Engrailed and Common emerald.
The best-known Rowan is Sorbus Aucuparia (European Rowan), a small tree of 15 x 7m tall and broad. It has dark green leaves that turn red and yellow in autumn. White flowers, borne in late spring, are followed by red-orange berries. The fruits are a favorite for many birds and are a traditional wild-collected food in Britain and Scandinavia. The berries can also be made into jelly, jam or other preserve, on their own, or with other fruits.
Sorbus glabrescens (White-fruited Rowan), 8-15 m tall, is a small and medium-sized deciduous tree native to Yunnan in China. The leaves are glaucous blue-green above and paler beneath, pinnate with 11-17 leaflets, with very fine serrated margins. The leaves change to orange or red in late autumn. In late spring to early summer, five-petaled white flowers with 20 yellowish-white stamens are produced in corymbs. The fruit is a pome of 8 mm in diameter, white color with a persistent pinkish carpel, borne on distinctively red fruit stalks. The fruits are matured in late autumn, persist long into the winter after leaf fall. The frost-softened fruits are then readily eaten by thrushes and waxwings, which disperse the seeds.
Sorbus alnifolia (Alder-leafed Whitebeam, Korean Whitebeam), 10-20 m tall, is a species of whitebeam native to eastern Asia, Korea, and Japan. It is a medium-sized deciduous tree with grey bark. The leaves are green above, and thinly hairy with white hair beneath. The leaves turn to orange-pink and red in autumn. The white flowers are 10-18 mm in diameter, five-petaled with 20 yellowish-white stamens, produced in corymbs of 4-8 cm diameter in late spring. The fruit is a bright red pome 8-15 mm in diameter, with a dimple at the apex, maturing in mid-autumn.
Sorbus domestica (Service Tree, True Service Tree), 10-20 m tall, is native to western, central and southern Europe. The bark is smooth on young trees, becoming fissured and flaky on old trees. The winter buds are green, with a sticky resinous coating. The leaves are pinnate, with 13-21 leaflets, and a bluntly acute apex. Half or two-thirds of the leaflets are with serrated margin. In late spring, the five-petaled white flowers with 20 creamy white stamens are produced in corymbs 10-14 cm in diameter. The flowers are hermaphrodite (having both male and female reproductive structures) and insect-pollinated. The fruit is a pome, 2-3 cm long, apple- or pear-shaped, greenish-brown, often tinged red with the side exposed to sunlight. This species is being listed as endangered in Switzerland and Austria, and uncommon in Spain.
Sorbus species grow well in sun or light shade, in fertile and well-drained soil. Propagation is by greenwood cuttings in summer. Fireblight is the disease known to affect Sorbus species.