Ailanthus altissima /eɪˈlænθəs ælˈtɪsɪmə/ ay-LAN-thəss al-TIH-sim-ə,[3] commonly known as tree of heaven, Ailanthus, varnish tree, copal tree, stinking sumac, Chinese sumac, paradise tree,[4] or in Chinese as chouchun (Chinese: 臭椿; pinyin: chòuchūn), is a deciduous tree in the family Simaroubaceae.[1] It is native to northeast and central China, and Taiwan. Unlike other members of the genus Ailanthus, it is found in temperate climates rather than the tropics.
The tree grows rapidly, and is capable of reaching heights of 15 metres (50 ft) in 25 years. While the species rarely lives more than 50 years, some specimens exceed 100 years of age.[5] Its suckering ability allows this tree to clone itself indefinitely.[6] It is considered a noxious weed and vigorous invasive species,[1] and one of the worst invasive plant species in Europe and North America.[7] In 21st-century North America, the invasiveness of the species has been compounded by its role in the life cycle of the also destructive and invasive spotted lanternfly.[8][9]
Description
Ailanthus altissima is a medium-sized tree that reaches heights between 17 and 27 m (60 and 90 ft) with a diameter at breast height of about 1 m (3 ft).[10] The bark is smooth and light grey, often becoming somewhat rougher with light tan fissures as the tree ages. The twigs are stout, smooth to lightly pubescent, and reddish or chestnut in color. They have lenticels and heart-shaped leaf scars (i.e., a scar left on the twig after a leaf falls) with many bundle scars (i.e., small marks where the veins of the leaf once connected to the tree) around the edges. The buds are finely pubescent, dome-shaped, and partially hidden behind the petiole, though they are completely visible in the dormant season at the sinuses of the leaf scars.[11] The branches are light to dark gray in color, smooth, lustrous, and contain raised lenticels that become fissures with age. The ends of the branches become pendulous. All parts of the plant have a distinguishing strong odor that is often likened to peanuts, cashews,[4] or rotting cashews.[12]
The leaves are large, odd- or even-pinnately compound on the stem. They range in size from 30 to 90 centimetres (1 to 3 ft) in length and contain 10–41 leaflets organised in pairs, with the largest leaves found on vigorous young sprouts. When they emerge in the spring, the leaves are bronze, then quickly turn from medium to dark green as they grow.[13] The rachis is light to reddish-green with a swollen base. The leaflets are ovate-lanceolate with entire margins, somewhat asymmetric and occasionally not directly opposite to each other. Each leaflet is 5–18 cm (2–7 in) long and 2.5–5 cm (1–2 in) wide. They have a long, tapering end, while the bases have two to four teeth, each containing one or more glands at the tip.[11] The leaflets' upper sides are dark green in color with light green veins, while the undersides are a more whitish green. The petioles are 5–12 millimetres (0.2–0.5 in) long.[4] The lobed bases and glands distinguish it from similar sumac species.
The flowers are small and appear in large panicles up to 50 cm (20 in) in length at the end of new shoots. The individual flowers are yellowish green to reddish in color, each with five petals and sepals.[10][4] The sepals are cup-shaped, lobed and united while the petals are valvate (i.e., they meet at the edges without overlapping), white and hairy towards the inside.[11][14][15] They appear from mid-April in the south of its range to July in the north. A. altissima is dioecious, with male and female flowers being borne on different individuals. Male trees produce three to four times as many flowers as the females, making the male flowers more conspicuous. Furthermore, the male plants emit a foul-smelling odor while flowering to attract pollinating insects. Female flowers contain 10 (or rarely five through abortion) sterile stamens (stamenoids) with heart-shaped anthers. The pistil is made up of five free carpels (i.e., they are not fused), each containing a single ovule. Their styles are united and slender with star-shaped stigmata.[11][14] The male flowers are similar in appearance, but they lack a pistil and the stamens do function, each being topped with a globular anther and a glandular green disc.[11] The fruits grow in clusters; similar to the ash tree (Fraxinus excelsior), the fruits ripen to a bright reddish-brown color in September.[16] A fruit cluster may contain hundreds of seeds.[7] The seeds borne on the female trees are 5 mm (0.2 in) in diameter and each is encapsulated in a samara that is 2.5 cm (1 in) long and 1 cm (0.4 in) broad, appearing July through August, but can persist on the tree until the next spring. The samara is large and twisted at the tips, making it spin as it falls, assisting wind dispersal,[10][4] and aiding buoyancy for long-distance dispersal through hydrochory.[17] Primary wind dispersal and secondary water dispersal are usually positively correlated in A. altissima, since most morphological characteristics of samaras affect both dispersal modes in the same way – except for the width of the samaras, which in contrast affects both types of dispersal in opposing ways, allowing differentiation in the dispersal strategies of this tree.[18] The females can produce huge numbers of seeds, normally around 30,000 per kg,[10] and fecundity can be estimated nondestructively through measurements of diameter at chest height.[17]