A large, deciduous, often unisexual tree, frequently 50 to 70 ft, rarely loo ft high, with a trunk 2 to 3 ft in diameter, and a rounded head of branches. The older bark is marked with numerous grey fissures. Leaves pinnate, from 1 to 11⁄2 ft long on adult trees (often twice as large on young ones), composed of fifteen to over thirty leaflets, foetid. Leaflets 3 to 6 in. long, ovate, pointed, widely cuneate to truncate or slightly retuse at the base; the margin entire except for one to three teeth on both sides near the base, each marked with a conspicuous gland; stalks 1⁄4 to 3⁄4 in. long. Flowers in terminal panicles, with male and female flowers as a rule on separate trees (but not always); greenish, the male ones evil-smelling. The fruit consists of one to three, sometimes five, keys like those of the ash, several hundreds of which are borne on large branching panicles 9 to 12 in. high and through. Each key (samara) is about 11⁄2 in. long, 1⁄2 in. wide, flat, thin, narrow-oblong, tapering towards both ends, with one seed in the centre. The keys are reddish brown, and a tree in full fruit is handsome. They have a peculiar twist at each end, which causes them to revolve with great rapidity as they fall. They are thus much longer reaching the ground, and in even a slight movement of the air will be carried a considerable distance. This is no doubt a provision to help in the dissemination of the seeds.
Native of N. China; introduced by Peter Collinson in 1751. It is hardy over most parts of the British Isles, but apparently succeeds best in the south of England. Few trees thrive so well in towns, but for planting there female trees should alone be used, owing to the objectionable odour of the male when in flower. For this purpose, the tree should be increased by root-cuttings taken from a female tree, as the sex of seedling plants cannot be determined until they are too big to transplant. Among pinnate-leaved trees of similar character, the ailanthus is easily recognised by the glandular teeth near the base of the leaflets. The generic name is derived from ‘Ailanto’, the native name for A. moluccana, signifying a tree tall enough to reach the skies. Hence also the popular name of ‘Tree of Heaven’. It is very effectively used as a fine-foliaged plant in summer by cutting young trees back to the ground in spring, and reducing the young shoots to one. Treated in this way, and given good soil, leaves 4 ft long are produced.
The tallest specimen recorded recently in the British Isles grows at Endsleigh in Devon (95 × 9 ft in 1963). Others of size are: Selborne, Dorset, 82 × 121⁄4 ft (1964), Westonbirt, Glos., 80 × 8 ft (1967), St James’s Park, London, 68 × 9 ft (1963).
cv. ‘Erythrocarpa’. – Leaves darker than in the type; fruits red. Described by Carrière in Rev. Hort., 1867, p. 419.
cv. ‘Pendulifolia’. – This has its branches erect as in the type, but the leaves, which are more than ordinarily long, hang downwards, rather than stand out horizontally as in the type. It also makes a bushier tree. It originated before 1889.
var. sutchuenensis (Dode) Rehd. & Wils. A. sutchuenensis Dode – This differs from the type in its glabrous, shining, reddish-brown young shoots, purplish leaf-stalks, also in the leaflets not being edged with fine hairs and wedge-shaped at the base. The winged fruits are 2 in. long, 1⁄2 in. wide. Originally found by Henry in Hupeh, afterwards by Farges in Szechwan. Introduced about 1897.
A. giraldii Dode – This species is of rather doubtful standing. Dode founded it on a specimen collected by Père Farges in E. Szechwan in 1893 and on young trees growing in French nurseries, raised from seed collected by French missionaries (probably by Farges himself and by Ducloux). The name chosen by Dode suggests that seed, or specimens, must also have been sent by the missionary Giraldi, who botanised in Shensi. Among the nurseries mentioned by Dode as having seedlings of this ailanthus was Messrs Chenault: but a tree at Kew received from that firm in 1907 as A. glandulosa giraldii has recently been examined and proves to differ in no botanical respect from A. altissima (glandulosa). This doubt has arisen too recently for it to have been possible to examine material from other cultivated trees.
A. giraldii is said to differ from A. altissima in leaves with larger, more numerous leaflets, more persistently downy on the undersides; longer panicles and larger fruits. The young wood is stated to be brown and the leaf-stalks purplish. In f. duclouxii Rehd., the young wood is described as light orange; leaf-stalks green; leaves less downy beneath except on the veins.