Trees & Shrubs – Sorbus
Formerly, when a wider variety of fruits were commonly eaten in European and North American culture, Sorbus counted among the home fruits.
Sorbus is a genus of about 100–200 species of trees and shrubs in the Rose family Rosaceae. Species of Sorbus (s.l.) are commonly known as whitebeam, rowan, service tree, and mountain-ash. The exact number of species is disputed depending on the circumscription of the genus, and also due to the number of apomictic microspecies, which some treat as distinct species but others group in a smaller number of variable species. Recent treatments treat Sorbus in a narrower sense to include only the pinnate leaved species of subgenus Sorbus, raising several of the other subgenera to generic rank.
Sorbus is unrelated to the true ash trees which belong to the genus Fraxinus, although the leaves are superficially similar.
As treated in its broad sense, the genus is divided into two main and three or four small subgenera (with more recent generic assignments in parentheses):
- Sorbus subgenus Sorbus (genus Sorbus s.s.), commonly known as the rowan (primarily in the UK) or mountain-ash (in both North America and the UK), with compound leaves usually hairless or thinly hairy below; fruit carpels not fused; type species Sorbus aucuparia (European rowan). Distribution: cool-temperate Northern Hemisphere. (Genus Sorbus s.s.)
- Sorbus subgenus Aria (genus Aria), the whitebeam, 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 (genus Aria), 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 (genus 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: North Africa, warm-temperate Europe, West Asia.
- Sorbus subgenus Torminaria (genus Torminalis), with rather maple-like lobed leaves with pointed lobes; fruit carpels not fused; just one species, Sorbus torminalis (Wild Service Tree). Distribution: temperate Europe, south to the mountains of North Africa and east to the Caucasus ranges.
- Sorbus subgenus Chamaemespilus (genus Chamaemespilus), a single shrubby species Sorbus chamaemespilus (false medlar) 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.
The RHS list the following Sorbus as native trees and shrubs.
Sorbus aria (whitebeam): 20m, attractive berries, good on chalk
Sorbus aucuparia (rowan): 15m, attractive berries and autumn foliage
Sorbus bristoliensis: 10m, woolly leaf undersides, orange fruits
Sorbus devoniensis: 15m, medium-sized brown berries
Sorbus domestica (service tree): 20m, pollution-tolerant, best on acid soils
Sorbus subcuneata: 10m, large, brown berries, not readily available
Sorbus torminalis (wild service tree): 20m, attractive autumn colour
Sorbus arranensis (Arran whitebeam): 7.5m, small fruits, narrow leaves
Sorbus eminens: 6m, large red fruit
Sorbus hibernica: 6m, small pink/red fruit, not readily available
Sorbus lancastriensis: 5m, large crimson fruit
Sorbus porrigentiformis: 5m, large leaves, small fruits
Sorbus pseudofennica (Arran service tree): 7m, elongated red berries
Sorbus rupicola: 6m, elongated leaves, deep red fruit
Sorbus vexans: 6m, not good on chalk, scarlet fruit
Sorbus wilmottiana: 6m, small leaves and fruit
Sorbus leptophylla (Welsh whitebeam): 3m, large scarlet fruit, not readily available
Sorbus leyana: 3m, small leaves and fruit
Sorbus minima: 3m, sparse shrub with scarlet fruit
Sorbus anglica (English whitebeam): 2m, good autumn colour
Naturally occurring hybrid Sorbus × vagensis
The 19th Century botanist A D Webster listed Sorbus as syn Pyrus with the following in his Hardy ornamental flowering trees & shrubs. Dates indicate introduction to Britain next to place of origin. Some species have since been re-classified.
PYRUS. (syn Sorbus)
PYRUS ARIA.—White Beam Tree. Europe (Britain). A shrub or small-growing tree, with lobed leaves, covered thickly on the under sides with a close, flocculent down. The flowers are small and white, and produced in loose corymbs. It is a handsome small tree, especially when the leaves are ruffled by the wind and the under sides revealed to view. The red or scarlet fruit is showy and beautiful. View London Tree Surgeons expanded page on the White Beam
P. AUCUPARIA.—Mountain Ash, or Rowan Tree. Too well-known to need description, but one of our handsomest small-growing trees, and whether for the sake of its dense corymbs of small white flowers or large bunches of scarlet fruit it is always welcomed and admired. P. Aucuparia pendula has the branches inclined to be pendulous; and P. Aucuparia fructo-luteo differs from the normal plant in having yellowish instead of scarlet fruit. View London Tree Surgeons expanded page on the Mountain Ash or Rowan.
P. AMERICANA (syn Sorbus americana).—American Mountain Ash. This species, a native of the mountains of Pennsylvania and Virginia (1782), is much like our Rowan Tree in general appearance, but the bunches of berries are larger, and of a brighter red colour.
P. ANGUSTIFOLIA.—North America, 1750. A double-flowered crab is offered under this name, of vigorous growth, bearing delicate pink, rose-like flowers that are deliciously fragrant, and borne contemporaneously with the leaves. The merits claimed for the shrub are perfect hardihood, great beauty of blossom and leaf, delicious fragrance, and adaptability to various soils. The single-flowered form extends over large areas in the Atlantic States of North America. They are very desirable, small-growing trees, and are described by Professor Sargent as being not surpassed in beauty by any of the small trees of North America.
P. BACCATA.—Siberian Crab. Siberia and Dahuria, 1784. This is one of the most variable species in cultivation, and from which innumerable forms have been developed, that differ either in habit, foliage, flowers, or fruit. The deciduous calyx would seem to be the only reliable distinguishing character. It is a widely-distributed species, being found in North China and Japan, Siberia and the Himalayas, and has from time immemorial been cultivated by the Chinese and Japanese, so that it is not at all surprising that numbers of forms have been developed.
P. CORONARIA.—Sweet Scented Crab. North America, 1724. This is a handsome species, with ovate, irregularly-toothed leaves, and pink and white fragrant flowers. The flowers are individually large and corymbose, and are succeeded by small green fruit.
P. DOMESTICA (syn Sorbus domestica).—True Service. Britain. This resembles the Mountain Ash somewhat, but the flowers are panicled, and the berries fewer, larger, and pear-shaped. The flowers are conspicuous enough to render the tree of value in ornamental planting. True Service
P. FLORIBUNDA (syns P. Malus floribunda and Malus microcarpa floribunda).—China and Japan, 1818. The Japanese Crabs are wonderfully floriferous, the branches being in most instances wreathed with flowers that are individually not very large, and rarely exceeding an inch in diameter when fully expanded. Generally in the bud state the flowers are of a deep crimson, but this disappears as they become perfectly developed, and when a less striking tint of pinky-white is assumed. From the St. Petersburgh gardens many very ornamental Crabs have been sent out, these differing considerably in colour of bark, habit, and tint of flowers. They have all been referred to the above species. P. floribunda is a worthy form, and one of the most brilliant of spring-flowering trees. The long, slender shoots are thickly covered for almost their entire length with flowers that are rich crimson in the bud state, but paler when fully opened. There are numerous, very distinct varieties, such as P. floribunda atrosanguinea, with deep red flowers; P. floribunda Elise Rathe, of pendulous habit; P. floribunda John Downie, very beautiful in fruit; P. floribunda pendula, a semi-weeping variety; P. floribunda praecox, early-flowering; P. floribunda mitis, of small size; P. floribunda Halleana or Parkmanii, probably the most beautiful of all the forms; and P. floribunda Fairy Apple and P. floribunda Transcendant Crab, of interest on account of their showy fruit. P. floribunda Toringo (Toringo Crab) is a Japanese tree of small growth, with sharply cut, usually three-lobed, pubescent leaves, and small flowers. Fruit small, with deciduous calyx lobes.
P. GERMANICA (syn Mespilus germanica).—Common Medlar. Europe (Britain), Asia Minor, Persia. Early records show that the Medlar was cultivated for its fruit as early as 1596. Some varieties are still grown for that purpose, and in that state the tree is not devoid of ornament. The large, white flowers are produced singly, but have a fine effect in their setting of long, lanceolate, finely-serrate leaves during May. View London Tree Surgeons expanded page on the Medlar or Common Medlar.
P. JAPONICA (syn Cydonia japonica).—Japanese Quince. Japan, 1815. This is one of the commonest of our garden shrubs, and one that is peculiarly well suited for our climate, whether planted as a standard or as a wall plant. The flowers are brilliant crimson, and plentifully produced towards the end of winter and before the leaves. Besides the species there are several very fine varieties, including P. japonica albo cincta, P. japonica atropurpurea, P. japonica coccinea, P. japonica flore-pleno, P. japonica nivalis, a charming species, with snowy-white flowers; P. japonica rosea, of a delicate rose-pink; and P. japonica princeps. P. japonica cardinalis is one of the best of the numerous forms of this beautiful shrub. The flowers are of large size, of full rounded form, and of a deep cardinal-rose colour. They are produced in great quantity along the branches. A well-grown specimen is in April a brilliant picture of vivid colour, and the shrub is sooner or later destined to a chief place amongst our ornamental flowering shrubs. P. japonica Maulei (syn Cydonia Maulei), from Japan (1874), is a rare shrub as yet, small of growth, and with every twig festooned with the brightest of orange-scarlet flowers. It is quite hardy, and succeeds well under treatment that will suit the common species.
P. PRUNIFOLIA.—Siberia, 1758. Whether in flower or fruit this beautiful species is sure to attract attention. It is a tree of 25 feet in height, with nearly rotundate, glabrous leaves on long footstalks, and pretty pinky-white flowers. The fruit is very ornamental, being, when fully ripe, of a deep and glowing scarlet, but there are forms with yellow, and green, as also striped fruit.
P. RIVULARIS.—River-side Wild Service Tree. North-west America, 1836. A native of North America, with terminal clusters of white flowers, succeeded by sub-globose red or yellow fruit, is an attractive and handsome species. The fruit is eaten by the Indians of the North-west, and the wood, which is very hard and susceptible of a fine polish, is largely used in the making of wedges. It is a rare species in this country.
P. SINICA (syn P. sinensis of Lindley).—Chinese Pear Tree. China and Cochin China, 1820. Another very ornamental Crab, bearing a great abundance of rosy-pink or nearly white flowers. It is a shrub-like tree, reaching a height of 20 feet, and with an upright habit of growth. Bark of a rich, reddish-brown colour. It is one of the most profuse and persistent bloomers of the whole family.
P. SINENSIS (syn Cydonia chinensis).—Chinese Quince. China, 1818. This is rarely seen in cultivation, it having, comparatively speaking, few special merits of recommendation.
P. SMITHII (syns Mespilis Smithii and M. grandiflora).—Smith’s Medlar. Caucasus, 1800. The habit of this tree closely resembles that of a Hawthorn, and although the flowers are only half the size of those of the Common Medlar, they are produced in greater profusion, so that the round-headed tree becomes a sheet of white blossom during May and June. The reddish-brown fruits are small for a Medlar, and ripen in October.
P. TORMINALIS.—Wild Service Tree. A native species of small growth, with ovate-cordate leaves, and small white flowers. P. torminalis pinnatifida, with acutely-lobed leaves, and oval-oblong fruit may just be mentioned. Wild Service Tree
P. VESTITA.—Nepaul White Beam. Nepaul, 1820. In this species the leaves are very large, ovate-acute or elliptic, and when young thickly coated with a white woolly-like substance, but which with warm weather gradually gives way until they are of a smooth and shining green. The flowers are borne in woolly racemose corymbs, and are white succeeded by greenish-brown berries as large as marbles.
Other species of less interest are P. varidosa, P. salicifolia, P. salvaefolia, P. Bollwylleriana, and P. Amygdaliformis. They are all of free growth, and the readiest culture, and being perfectly hardy are well worthy of a much larger share of attention than they have heretofore received.