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.