My first introduction to a tree known as Tree of Heaven, Ailanthus altissima, was when I saw a large thicket of them next to a church parking lot near Hiram, Georgia. I’m not kidding. One tree was very slender and tall, in character with its Indonesian Ambonese name of ailanto, which means “heaven tree”, or “tree reaching for the sky”. After I made pictures and gathered samples, I headed home to make notes on what I thought was a hard to find species. Ironically, later the same day I discovered several more thickets of this same species very near my house. It seemed they were everywhere, but before then I had noticed none.
Common names for Ailanthus altissima are amusing: ailanthus, tree of heaven, Chinese sumac, China sumac, stinking sumac, stink tree, ghetto palm, and tree of hell. The names copal tree and varnish tree are found in some references, but these names more properly belong to other tree species. My favorite name for this tree is stink tree, due to its unpleasant odor resembling rotting peanuts. Though cut wood of many trees have an unpleasant smell, this tree’s odor is particularly unpleasant and is observed when branches and twigs are broken, leaves are crushed, or when the tree is flowering. Trees closely resemble sumac in appearance, but they can be easily distinguished. The name ghetto palm came from the tree’s presence in urban environments and abandoned mining and industrial sites where pollution and soil 
conditions would be too difficult for most other trees to live. People trying to contain this tree’s extremely resilient and invasive nature sometimes derisively call it tree of hell. Native to northeast and central China and Taiwan, it is a popular tree there serving many useful purposes. Even so, a common name for it there translates as ‘foul smelling tree’.
Ailanthus, or tree of heaven, is a fast-growing tree that can grow 90 feet high and have a trunk diameter of 40 inches. Growth of 3 to 6½ feet per year in the first years is considered normal, and leaves of vigorously growing younger trees are larger than those of older trees. Stump sprouts have even more vigorous growth, as evidenced by measurements of one researcher who recorded growth of 1 inch per day, 
totaling 12.6 feet in a season. Individual trees rarely live more than 50 years and some may live over 100 years, but due to remarkable suckering ability it is possible for a tree to clone itself indefinitely, in thickets. Roots can be a problem for nearby sidewalks, foundations, and sewer pipes, and they are often seen exposed on the surface. Bark is smooth and light gray, and it becomes rougher with light tan fissures as the tree ages. It is not unusual to see a small section of bark peeled off on larger trees. Twigs are very stout and chunky. They are smooth to lightly pubescent, are light chestnut in color, and have lenticels. Leaf scars are very large and shield-shaped. Buds are 
rounded and finely pubescent, and partly hidden behind the petioles. Branches are light to dark gray, and smooth with pronounced lenticels that become fissures with age. Fallen small branches are often seen about the tree, as they are very easy to break off. All parts discussed have a strong odor when broken, usually likened to rancid or rotting peanuts or cashews.
Leaves of ailanthus are pinnately compound, ranging from 1 to 4 feet in length. They are arranged alternately on stems. Each leaf is a rachis holding 10 to 41 leaflets, arranged in pairs. The rachis is light to reddish-green, it has a swollen base, and the pairs are usually directly opposite-but not always. Petioles holding leaflets 
are ¼ to almost ½ inch long. Leaflets measure 2 to 7 inches in length and 1 to 2 inches in width, are ovate-lanceolate, and have smooth margins. They have long tapering ends, and near each base are 2 to 4 (or possibly more) teeth with one or more glands at the tip. The presence of glandular teeth on leaflets help distinguish ailanthus from leaflets of sumac, which does not have such teeth. The upper leaflet surface is dark green, and the lower surface is lighter. Autumn leaf color is yellow.
Flowers of ailanthus appear in spring, in panicles that are longer in male trees than female trees. They are yellowish green to reddish green, and each flower has 5 petals and 5 sepals. The sepals are cup-shaped and the petals meet at the edges 
without overlapping. Male trees produce 3 to 4 times as many flowers as female trees, and emit a foul-smelling odor to attract pollinating insects. The fruit produced by female trees is in clusters of hundreds of seeds. They appear in late summer to early fall, but they can persist through the winter. Each seed is about 1/5 inch in diameter, encapsulated in a samara called a schizocarp that is about 1 to 1½ inch long and about 2/5 inch wide. The samara is twisted at the tip, making it spin as it falls. Individual trees may produce an estimated 325,000 seeds per year.
Despite its drawbacks, tree of heaven can be a useful tree. In China and Taiwan, it is the host plant for the Samia cynthia silkworm, which produces silk known as pongee, eri, and Shantung 
silk. This silk is stronger and cheaper than that produced using mulberry trees, but it has inferior gloss and texture and it is unable to take dye. The wood is hard when dry, but it dries unevenly producing cracks. When dried with special care, it is useful for the manufacture of furniture and cabinets, and kitchen steamers. In Chinese traditional medicine, almost all parts of the tree are used in various treatments. The tree produces the chemical ailanthone, which is allelopathic and inhibits growth of surrounding plants. Research indicates that when extracted, this chemical is a very effective herbicide and may possibly have agricultural applications in the future.
When brought to Europe and America in the 
1700’s, tree of heaven was an exotic ornamental that found uses as garden specimens, as quick-growing shade trees, and as street trees. It quickly spread outside its desired range, and today it can be found in thickets throughout the United States. It is now considered an invasive and unwanted species in most countries of the world, especially those having temperate climates. Tree of heaven is one tree best left in its native land.
