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Published In: Journal of the Washington Academy of Sciences 6(14): 495. 1916. (J. Washington Acad. Sci.) Name publication detailView in Biodiversity Heritage Library

Project Name Data (Last Modified On 9/22/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced


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1. Ailanthus altissima (Mill.) Swingle (tree-of-heaven, cancer tree, stinkweed)

Pl. 561 a–c; Map 2610

Plants small mostly medium-sized trees to 20 m tall (but frequently flowering when much smaller), incompletely dioecious, colonial from root suckers with age. Trunks 1 or few, stout, the bark light grayish brown, initially relatively smooth, eventually developing thin, pale grooves and thin, darker ridges. Twigs stout, tan to reddish brown with numerous, slender, pale lenticels and large, prominent, more or less kidney-shaped leaf scars, minutely hairy (difficult to see without magnification) the winter buds axillary (sometimes appearing asymmetrically terminal), depressed-globose, with several broadly rounded scales, densely short-hairy. Leaves (20–)40–100(–130) cm long, relatively short-petiolate. Leaf blades pinnately compound with (7–)11–41 leaflets (the terminal leaflet sometimes reduced or absent), these opposite, lanceolate to oblong-lanceolate or narrowly oblong-ovate, the lateral ones often somewhat curved toward the leaf tip, rounded to shallowly cordate and (at least the lateral ones) usually somewhat asymmetrical at the base, tapered to a sharply pointed tip, the margins entire or with 1–3(–5) pairs of blunt teeth toward the base, sometimes also hairy, the surfaces sparsely to moderately short-hairy and also with scattered, minute glands, especially near the midvein, sometimes becoming nearly glabrous with age, the upper surface dark green, the undersurface pale or lighter green. Inflorescences terminal, large, diffusely branched panicles, lacking bracts, the numerous, individually stalked flowers solitary or in small clusters along the ultimate branches, each cluster subtended by a pair of minute, linear, reddish bracts that are shed before the flowers open. Flowers mostly functionally imperfect, but often the pistillate ones appearing perfect by production of stamenlike staminodes. Calyces of (4)5 sepals, these 0.8–1.2 mm long, free or fused at the base, triangular, spreading with ascending tips, often persistent at fruiting. Corollas of (4)5 petals, these 2–4 mm long, narrowly oblong-elliptic, somewhat concave (scoop-shaped), green to greenish yellow, the upper surface (and basal portion of the margins) densely and minutely woolly. Staminate flowers with (8)10 stamens; pistillate flowers with 3–5 stamenlike staminodes, these rarely absent. Nectar disc present, irregularly lobed, dark purple to purplish brown. Pistillate flowers with the ovary of 2–5 carpels, 2–5-locular and lobed at flowering, the placentation axile; absent or rudimentary in staminate flowers. Style 1 per flower, with twisted, longitudinal lines equal to the carpel number, the stigma capitate and deeply 2–5-lobed. Fruits technically schizocarps, but through separation of the carpels appearing as small clusters of 2–5 samaras (sometimes only a solitary samara developing), these sessile, 3.0–5.5 cm long, 7–13 mm wide, narrowly oblong-elliptic (usually with a shallow, broad, median notch along 1 side), often somewhat spirally twisted toward the tip, usually strongly dark reddish-tinged at maturity, but becoming straw-colored to tan before dispersal. Seed 1 per samara, positioned near its midpoint, 5–8 mm long, ovate, strongly flattened, the seed coat fused to the samara wall. 2n=80. May–June.

Introduced, scattered, mostly south of the Missouri River, most abundantly in and around urban areas (native of Asia, introduced nearly throughout the U.S., also Canada, Mexico). Bottomland forests, mesic upland forests, banks of streams and rivers, and bases of bluffs; also old mines and quarries, fencerows, railroads, roadsides, and disturbed areas.

Tree-of-heaven is fast-growing and has been planted widely as a street tree, as a shade tree in yards, and as a soil binder in eroded areas or recovering strip mines. It is disease-resistant and also survives well in areas with high levels of air pollution. It was an inspiration for the popular novel A Tree grows in Brooklyn by Betty Smith (1943), in which the tree is a metaphor for the heroine, a young woman who manages to flourish under difficult circumstances.

Ailanthus altissima mainly becomes naturalized in highly disturbed areas, but in Missouri and some other states it occasionally becomes strongly invasive in forests. Once established, the species is very difficult to control or eradicate, resprouting readily from remaining roots after the aboveground portions have been killed by application of herbicides or mechanical removal. The relatively high growth rate and ability to sucker from roots allows the species to efficiently colonize forest margins and areas disturbed by tree falls. Established trees also produce allelopathic compounds, principally the quassinoid triterpenoid, ailanthone, that inhibit the germination and growth of neighboring plants of other species (Heisey, 1990a, b, 1996; J. G. Lawrence et al., 1991). The leaves and twigs, emit a disagreeable aroma when bruised or crushed, and the staminate flowers also are malodorous. Contact with the plants can cause dermatitis in some individuals and the plants reputedly are toxic when ingested (Burrows and Tyrl, 2001), but the strong bitter flavor makes it unlikely that the plant would be eaten in quantity. Bisognano et al. (2005) described a case in which absorption of the sap through an open wound resulted in myocarditis (inflammation of the heart muscle) in a person working as a tree surgeon.



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