A large family of hardy, small or medium-sized trees indispensable in the garden for their flower, attractive foliage, berry and autumn-colouring leaf. In the main, they have an elegant and compact habit of growth. For our purposes the sorbus may be conveniently divided into two groups — the whitebeams (aria group) and the mountain ashes or rowans (aucuparia group).
All species and varieties will thrive in any fertile soil, but the whitebeams are notably successful on chalk and limestone and the rowans happiest and longest lived on light neutral or acid soils. The following species and varieties are among the best of the many available today. S. commixta (aucuparia group), a Japanese species, also of upright habit, is notable for the brilliant flame or scarlet autumn colouring of its leaves and for the freely produced orange-red fruits. The variety Joseph Rock (aucuparia group) is an outstanding introduction from China and an ideal small garden tree of dense narrow habit. The pinnate leaves assume rich autumn tints of red, orange, bronze and purple, making an excellent background for the amber-yellow fruits.
Sorbus aria, whitebeam, a small to medium-sized round-headed European tree, with oval or obovate dentated leaves, green above and vivid white beneath. The spring flowers, although dull white, are heavily scented. In autumn, bright red fruits are produced in quantity; it is tolerant of wind and maritime exposure and is best represented in small gardens by one of its varieties. Decaisneana ( majestica) is the largest-leaved whitebeam with elliptical leaves up to 6 in. long and 4 in. wide and with larger fruits than in the type. The best whitebeam is lutescens, a variety which is particularly effective in spring and early summer, when its new leaves are downy white on both surfaces. S. hupehensis (aucuparia group) is a distinct and beautiful Chinese species, forming a compact head of ascending branches. The foliage is of an unusual blue-green hue, acting as a perfect foil for the white or pink-tinted fruits, which are produced in drooping clusters, and persist well into winter. The varieties obtusa and rosea are equally worthy variants with pink fruits.
The Swedish whitebeam, S. intermedia (aria group), is a very hardy small or medium-sized tree useful in exposed or bleak situations. The distinct leaves are lobed towards the base, green above and grey felted beneath. The large orange-red fruits are conspicuous in autumn.
S. pohuashanensis (conradinae) (aucuparia group), the Chinese rowan, is a hardy and robust small or medium-sized tree, spectacular in autumn when laden with heavy bunches of large orange-red fruits. A choice Chinese species, S. sargentiana (aucuparia group) slowly attains about 25 ft. The sticky winter buds are reminiscent of those of the horse chestnut (aesculus). The handsome pinnate leaves, among the largest of the genus, colour magnificently a rich red in the autumn.
S. aucuparia, the rowan or mountain ash, is a familiar European species forming a small or medium-sized tree, usually of erect habit. In marked contrast to those of the whitebeam, the leaves are pinnate, 5 to 9 in. long, and composed of up to nineteen leaflets. The flat terminal white flower heads 3 to 5 in. across, which open in late spring, are followed by quantities of scarlet berries. There are a number of equally worthy garden varieties; Sheer-water Seedling, a recent introduction of narrow, upright and compact habit, is ideal as a street tree or for a restricted site in the small garden. The foliage is an attractive blue green and the fruits orange scarlet in large clusters. The variety xanthocarpa (fructuluteo) has golden-yellow fruits which are less attractive to birds.
A small tree from western China, S. scalaris (aucuparia group) is distinct in its wide-spreading head, and in its unusual
A very graceful, medium-sized tree, T. euchlora ( cordata x dasystyla) has lower branches which are pendulous on older specimens while immature trees have arching branches and bright glossy green leaves. This hybrid is free from aphid (greenfly) attack — a troublesome complaint of many limes.
The weeping silver lime, T. petiolaris (americana pendula), forms a most graceful and beautiful tall weeping tree, with a rounded head and downward-sweeping branches. The long-stalked leaves are white felted beneath, and in a breeze add considerably to the attraction of this fine tree. The heavily scented flowers produced in late summer are regrettably narcotic to bees.
Platyphyllos, the broad-leaved lime, becomes a large and rapid-growing tree of rounded habit, now much planted in parkland or public places instead of T. europaea, the common lime, which has a densely suckering habit. Its variety T. p. rubra, the red-twigged lime, has the additional attraction of red-brown winter shoots, and a more upright habit of growth.
Dark glossy green fern-like leaves with grey downy undersides. The orange fruits are freely produced and the foliage turns crimson and purple in autumn.
S. vilmorind is an elegant and delightful small tree from western China. In late summer and autumn the branches are hung with clusters of rosy-red fruits which turn pink and finally fade to white, tinted pink. This is an excellent tree for the smallest garden.