Forest Preserve District of Cook County, Illinois
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The Ailanthus
Nature Bulletin No. 563-A   April 19, 1975
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

THE AILANTHUS
One of the depressing aspects of congested areas in a big city is the almost total absence of trees. Either they are poisoned or they are starved for food, water and light. Smoke and fumes, dust and grime, refuse and ashes, cinders and salt, make it impossible for our native trees to survive -- especially when the soil around them is covered with pavement or packed by trampling feet. But some people living in such neighborhoods, and instinctively yearning for a green growing tree, have found one kind that will thrive even under those conditions: the Ailanthus.

Over two centuries ago it was brought from China to Europe; and then in the early 1800's, to America. Ailanthus is the Latinized form of "ailanto," a native word of the East Indies, meaning Tree of Heaven -- a tree that overtops other trees. Its scientific name is Ailanthus altissima, the latter word meaning "very tall. " Its nearest relatives are eight or nine trees and shrubs of Asia and Australia. They belong to the Quassia family named after a tree of the New World tropics, whose wood is used in the drug industry.

Notable for its handsome foliage, the ailanthus is a rapidly growing tree that becomes rather large with a spreading crown of a few main branches and smooth striped bark. The wood is weak, soft and of little use. The twigs are coarse and have exceptionally large leaf scars with a prominent bud in a notch on the upper side. The leaves are alternate, very long, pinnately compound with from 13 to 25 leaflets each, and have a strong unpleasant odor when bruised.

Huge loose clusters of small greenish-yellow flowers appear in June or July, the male and female flowers being on separate trees. The male pollen-producing flowers have such a disagreeable powerful smell that male trees are seldom planted or allowed to grow. The mature female trees bear great masses of seeds that are very showy at first -- yellow tinged with crimson. Each seed has an inch-long twisted wing at either end. Months later, when brown and dry, they snap off in the wind and spin away like little airplane propellers.

One such tree can scatter seeds for blocks around and, because they seem to be able to germinate and grow almost anywhere, the ailanthus is like a weed. Seedlings pop up in lawns, gardens, hedges, around the foundations of buildings, in roof gutters, and even take root in crevices of brick or concrete walls. Not only that: around one of these prolific trees a thicket sprouts from its wide-spreading roots. If one is cut down without grubbing out the roots, it may grow again and, a year later, be ten feet tall.

The ailanthus has become naturalized and now grows wild around many big cities. It is remarkably free from diseases and insect pests. However, in the Orient its leaves are the preferred food of the ailanthus silk. moth, a near relative of the Cecropia, one of the largest of our native moths. It is raised to produce silk but is far different from the common domesticated silkworm which feeds on mulberry leaves. The silk unwound from its cocoons wears much better than that of the common silkworm but is not so soft and glossy. In China, a man's coat made of ailanthus silk may have been worn by his father and grandfather before him. Its commercial production was tried in France and, in 1861, in the United States but abandoned because of the excessive hand labor required.

In America, the ailanthus is the "Tree of Cities. "


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