Ailanthus altissima

• 1. Introduction

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  In 1886, the city of Atlanta, Georgia, wrote an ordinance about a single kind of tree. Ailanthus altissima, known as the tree of heaven, was declared a public nuisance. Anyone who owned or occupied a lot where one grew faced a fine of 50 dollars. The city's Street Committee was given the power to destroy every one growing on city property.

  That was an odd fate for a tree whose common name promises paradise. Today it grows on every continent except Antarctica. How did one tree gather so many reputations, from garden treasure to civic enemy? Why did botanists spend decades unable to agree on what to call it? And what makes it so stubborn that cities and countries still struggle to remove it?

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• 2. A Name Nobody Agreed On

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  In the 1740s, a French Jesuit named Pierre Nicolas d'Incarville packed seeds in Peking and sent them across Siberia to his friend, the botanist Bernard de Jussieu. D'Incarville believed they came from the Chinese varnish tree, Toxicodendron vernicifluum, which he had seen in the lower Yangtze region. He said so in a note attached to the package. That note caused years of confusion, because the seeds actually came from the tree of heaven.

  In 1751, Jussieu planted a few of the seeds in France. He sent others to Philip Miller, the superintendent of the Chelsea Physic Garden, and to Philip C. Webb, who kept an exotic plant garden in Busbridge, England. All three men gave the plant a different name. In Paris, Linnaeus called it Rhus succedanea, while the public knew it as grand vernis du Japon. In London, Miller named it Toxicodendron altissima. At Busbridge it was labelled Rhus Sinese foliis alatis under the old classification system.

  Records from the 1750s show Miller disputing the proper name with John Ellis, the curator of Webb's garden. Nothing was settled. In 1782, Jakob Friedrich Ehrhart noticed a specimen in Utrecht and added yet another name, Rhus cacodendron.

  Clarity arrived in 1788. René Louiche Desfontaines studied the winged seeds, called samaras, on the Paris trees, which still carried the label Rhus succedanea. He concluded that the plant was not a sumac at all. He published an illustrated description under the name Ailanthus glandulosa, placing it beside a tropical species then called A. integrifolia. The word glandulosa pointed to the glands on the leaves. It survived until as late as 1957, when it was ruled invalid as a later homonym at the species level.

  The accepted name came from Walter T. Swingle, who worked for the United States Department of Plant Industry. He took Miller's older species name and moved it into Desfontaines' genus. The result was Ailanthus altissima. The genus now holds five other species from east Asia and Australia, all in the quassia family, Simaroubaceae. A long table of synonyms still records the earlier attempts, reaching back to Toxicodendron altissimum in 1768.

  The genus name has a different origin. It comes from ailanto, an Ambonese word meaning heaven-tree or tree reaching for the sky. Ambonese speakers use it for the evergreen Ailanthus integrifolia. Altissima is Botanical Latin for tallest. The English name tree of heaven has been in use since 1845.

  English common names are a tangle. Chinese sumac, varnish tree, copal tree, stinking sumac and paradise tree all belong to other plants as well. People in poorer neighbourhoods, where the tree grows thickly, have mocked it as the ghetto palm. Gardeners and conservationists fed up with its unruly habits call it the tree of hell.

  Swingle's choice kept Miller's altissima, Latin for very tall. The growth records show why the word fits.

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• 3. Anatomy of a Sprinter

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  A mature Ailanthus altissima stands between 17 and 27 metres tall, with a trunk about one metre across at breast height. Its bark is smooth and light grey, roughening into pale tan fissures with age. The twigs are stout and reddish or chestnut, and they carry heart-shaped scars where leaves once attached. Every part of the plant gives off a strong smell, which people have compared to peanuts, cashews, or rotting cashews.

  The leaves are enormous. They measure 30 to 90 centimetres long and hold between 10 and 41 leaflets arranged in pairs, with the biggest leaves on vigorous young sprouts. They emerge bronze in spring and quickly darken to green. Two to four teeth at the base of each leaflet end in glands. Those lobed, gland-tipped bases help botanists tell the tree apart from similar sumac species.

  In mid-April in the south of its range, and as late as July in the north, the tree flowers. The blooms form panicles up to 50 centimetres long at the tips of new shoots. Individual trees are either male or female. Males produce three to four times as many flowers as females, and they give off a foul odor while in bloom to draw pollinating insects.

  The female trees do the long-distance work. Their fruit clusters ripen to a bright reddish-brown in September, and one cluster can hold hundreds of seeds. Each seed is about 5 millimetres across and sits inside a samara 2.5 centimetres long and 1 centimetre broad. The samara is twisted at the tips, so it spins as it falls and the wind carries it away. It also floats, which allows water to move the seed further. The same shape serves both jobs, although the width of the samara pulls the two kinds of dispersal in opposite directions.

  Seeds are so plentiful that females produce around 30,000 per kilogram. The tree's growth is just as startling. Gains of 1 to 2 metres a year for the first four years are normal, and the species may be the fastest-growing tree in North America. A tree can reach 15 metres in 25 years. Trees in California outgrew those on the East Coast, and American trees generally outgrew Chinese ones.

  The sprint comes at a cost. Most trees live only 30 to 50 years, although healthy seed-producing individuals older than 100 have been found in studies. In Europe the trunks often hollow out with no outward sign before high winds bring them down.

  Researchers can even estimate how many seeds a female will release, simply by measuring the diameter of her trunk.

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• 4. Chemistry and Endurance

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  In one laboratory test, a crude extract of ailanthus root bark stopped half of a batch of garden cress seeds from germinating. The same study used the extract as a herbicide on seven crop and weed species, including pea, maize, redroot pigweed and barnyard grass. It killed nearly 100 percent of the seedlings. Only velvetleaf showed some resistance.

  The active agent is ailanthone, an allelopathic chemical that inhibits other plants. It is strongest in the bark and roots but also occurs in the leaves, wood and seeds. A separate experiment found that a water extract was lethal or highly damaging to 11 North American hardwoods and 34 conifers. White ash was the only plant tested that escaped harm.

  The tree's own seedlings are unaffected, which suggests a defence against poisoning itself. Resistance in other species grows with exposure, and seeds from exposed plants resist better than those from unexposed ones. Populations meeting the chemical for the first time are the most vulnerable. Along highways, the toxin helps explain why the tree forms dense thickets with few other species among them.

  The tree also demands very little. It thrives in full sun and disturbed ground. A study in an old-growth hemlock and hardwood forest in New York found that it could still compete in canopy gaps receiving only 2 to 15 percent of full sunlight. Researchers called its approach gap-obligate, meaning it grows fast in one short burst instead of slowly over decades.

  Pollution seems to bother it little. Among trees, ailanthus is one of the most tolerant of sulfur dioxide, which it absorbs through its leaves. It resists cement dust, coal tar fumes and ozone, and high concentrations of mercury have been found in its tissues. It has been used to restore ground damaged by acid mine drainage. It tolerates a pH as low as 4.1, roughly that of tomato juice, along with very low phosphorus and high salinity. Roots that store water make it strongly drought-hardy, and they are strong enough to damage buried sewers and pipes.

  In northern Europe, the tree was not counted as naturalised in cities until after the Second World War. The explanation is rubble, because it colonised the ruins of destroyed buildings where most plants could not grow. It also needs warmth, with a mean annual temperature of about 8 degrees Celsius for good growth, and cities run warmer than the countryside. A German study found it in 92 percent of densely populated areas of Berlin, 25 percent of the suburbs, and only 3 percent of the land outside the city.

  In Hungary, where the climate is mild enough, it has moved beyond the cities. It has colonised natural areas there, and it is considered a threat to biodiversity in Aggtelek National Park.

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• 5. Across the Oceans

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  In 1784, a Philadelphia gardener named William Hamilton received seeds that had been forwarded from England, and the tree reached the United States. It arrived while chinoiserie dominated European arts, and gardeners initially hailed it as a beautiful specimen. In both Europe and America it became a favorite street tree, and by 1840 most nurseries stocked it. Enthusiasm cooled once gardeners learned about its suckering habit and its stench. Even so, it lined streets for much of the 19th century.

  The tree followed people. Chinese immigrants carried it to California during the Gold Rush of the 1850s. Its earliest introductions outside China were to southern Korea and Japan, though it may be native in those places. Inside China, it has also spread beyond its home range into Qinghai, Ningxia and Xinjiang.

  By the 20th century, the fashion had reversed. In 1982, the horticulturalist Michael Dirr of the University of Georgia met a grower who could not find a single buyer. Dirr wrote that "for impossible conditions this tree has a place." Nurseries once avoided the odor by selling only female plants, since only males produce it, but that choice meant more seed. In Europe the tree is still planted in gardens to some degree. It is especially common in London squares, streets and parks, and in German gardens. Named cultivars include Hongye, meaning red leaves, Metro, a male with a tighter crown, Erythrocarpa with red fruits, Pendulifolia with long hanging leaves, and Thousand Leaders.

  Everywhere it was planted, the tree escaped cultivation, and the United States saw the most extensive escape. In Europe it has naturalised as far east as Ukraine and Poland. Every continental country to the west has it except the Netherlands and Denmark. It also grows across Great Britain.

  Farther afield, it has naturalised on the southern shore of the Mediterranean in Morocco, Algeria, Tunisia and Libya, but not in Egypt. In the Middle East it grows in Jordan and Iraq and north into the northern Caucasus. Botanist Michael Hassler lists it as native to India, Pakistan, Vietnam, the Solomon Islands and several Indonesian islands, which contradicts other sources that call it introduced there.

  In Oceania, it is listed as a weed in New South Wales and Victoria and is present in six Australian states or territories altogether. New Zealand names it on its 2020 National Pest Plant Accord and its 2024 environmental weeds list. In Hawaii, it was first planted in 1924. South of the Sahara it occurs only in South Africa and Lesotho, and South Africa requires it to be controlled, or removed and destroyed. In South America it grows in northern Argentina, Uruguay, central Chile and the Juan Fernández Islands.

  In North America the range runs from Massachusetts west to southern Ontario, southwest to Iowa, south to Texas and north Florida. In the west it stretches from New Mexico to California and north to Washington. In the east it thrives in disturbed urban ground where it was once planted along streets. A 2003 study in North Carolina tied it more closely to railways and highways than to rivers. A survey in southwestern Virginia found it thriving along roughly 30 percent of the state's interstate highway system. In the mountainous West it clusters around old dwellings and abandoned mining operations. National Forest System lands classify it as noxious or invasive.

  For a tree that began as seeds in a Jesuit's package, the scale of its spread is the main reason it has been declared a weed in so many countries.

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• 6. Silk and Steamers

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  The Yantai region of Shandong, in China, is particularly well known for a coarse, hard-wearing silk that will not take dye. The silk comes from the moth Samia cynthia, whose caterpillars feed on ailanthus leaves. It goes by several names, including pongee and eri silk. Shantung silk takes its name from Shandong, where much of it is made. The tree has been grown widely in China and elsewhere to feed these caterpillars, and the moth has been introduced into the United States.

  The wood has its own trade. It is pale yellow, close-grained and satiny, and cabinet makers once used it. It is flexible enough for kitchen steamers, which are essential in Chinese cooking of mantou, pastries and rice. Zhejiang in eastern China is the region most famous for making them. Across much of its range the wood also serves as firewood, since it is moderately hard and heavy and easy to find. It is also turned into charcoal for cooking.

  As lumber it causes trouble. The fast early growth leaves the trunk with an uneven texture between inner and outer wood, and boards can twist or crack as they dry. Drying techniques now prevent the cracking, so the wood can be harvested commercially. The living tree is very flexible, yet the properly dried wood is quite hard.

  In medicine, nearly every part of the tree has been used in Chinese traditional practice. Roots, leaves and bark are used mainly as an astringent. American herbalists in the 19th century made a tincture from the root bark. The same tinctures were known to cause nausea, vomiting and muscle weakness. The tree's odors have been linked to nausea and headaches. Contact dermatitis has been reported in humans and in sheep, and the sheep developed weakness and paralysis.

  The plant contains quassin, saponin and ailanthone, along with a quinone irritant called 2,6-dimethoxybenzoquinone. According to Elbert Luther Little, the roots are poisonous to humans. Illness has also been reported after eating other plant parts and after drinking water contaminated by the flowers. In rare cases, workers clearing heavily infested ground developed myocarditis, an inflammation of the heart, after exposure to the sap. Goats, however, fed leaves for over 100 days showed no ill effects. They avoided the bark, yet extracts from it did them no harm.

  Another insect that feeds on the tree was first seen in the United States in 2014, and it brought far worse trouble than silk.

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• 7. Pests and Control

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  The ailanthus webworm, Atteva aurea, is an ermine moth native to Central and South America. It originally fed on other members of the mostly tropical quassia family, and in North America it turned to the tree of heaven. Elsewhere, the leaves feed the Indian moon moth, cobra moths and the common grass yellow. In the United States the tree has also hosted the brown marmorated stink bug and the Asiatic shot-hole borer. In its native range it is associated with at least 32 species of arthropods and 13 species of fungi.

  The spotted lanternfly, Lycorma delicatula, is the host-dependent troublemaker. It prefers the tree to complete its life cycle but does not strictly need it. It may absorb quassinoid compounds from the tree and use them as a chemical defense against birds. The insect has spread from southeastern Pennsylvania to 17 eastern states, damaging orchards, vineyards and forests.

  Because lanternflies are drawn to the tree, removing it is an important way to reduce their numbers in an area. The same attraction lets officials use the trees to detect lanternflies in new places. Managers also treat selected trap trees with insecticide, which cuts the insect's population while limiting harm to other species.

  Controlling the tree itself is hard because cutting it makes it resprout rapidly. The city of Basel in Switzerland runs an eradication program. Methods can be physical, thermal, managerial, biological or chemical, and combinations work best if they are compatible. The most effective regimen usually mixes chemical and physical control. Foliar or basal herbicides kill existing trees, while hand pulling or mowing stops seedlings.

  Policy has moved well beyond local programs. The European Union lists the tree among invasive alien species of Union concern, and no member state may import, breed, transport, sell or deliberately release it.

  Biological control is still under study. Research on verticillium wilt, caused by Verticillium nonalfalfae, has uncovered a strain that preferentially attacks ailanthus. As of 2024, no commercial bioherbicide has been developed.

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• 8. Heaven in Literature and Art

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  The Erya, the oldest surviving Chinese dictionary, was written in the 3rd century BCE and lists the tree second among its trees. A materia medica compiled during the Tang dynasty in 656 CE mentions it again. The two works favoured different characters, and Chinese botanists still debate which one is correct. The present name, chouchun, means stinking tree and is a relatively recent label. Near the lower Yellow River it is called chunshu, or spring tree, because it is one of the last trees to leave dormancy. Its leaves signal that winter is truly over.

  Chinese literature uses it for two extreme metaphors. A mature tree stands for a father, and a stump stands for a spoiled child. In a letter, a writer may wish that a friend's "Ailanthus and daylily are strong and happy," meaning the friend's father and mother. A parent may scold a child as a "good-for-nothing Ailanthus stump sprout." That insult descends from the Taoist philosopher Zhuangzi, who described a tree grown from a stump sprout and too irregular for carpentry. Later scholars linked it to ailanthus and applied it to children who ignore rules and tradition.

  In 1931, William Faulkner placed a "heaven-tree" outside the Jefferson jail in his novel Sanctuary. Its shadow hangs over a condemned prisoner and the spirituals sung in the street below.

  Betty Smith made the tree her central metaphor in the 1943 novel A Tree Grows in Brooklyn. She wrote: "No matter where its seed falls, it makes a tree which struggles to reach the sky." She added that it "is the only tree that grows out of cement." Gordon Young's 2013 book Teardown: Memoir of a Vanishing City uses it to describe the Carriage Town neighborhood in Flint, Michigan. He jokes that it earned its name "perhaps because only God can kill the things."

  In 1975, the sculptor Isamu Noguchi bought a building in the Astoria section of Queens, New York City, that later became the Noguchi Museum. While cleaning up the back lot, he left one tree standing, a tree of heaven. Staff ate lunch beneath it. The former aide and later curator Bonnie Rychlak said that "in a sense, the sculpture garden was designed around the tree." Until the 26th of March 2008, the 60-foot tree was the centerpiece of the garden. By then it was dying and threatened to fall onto the building, which was about to undergo major renovation. The museum hired the Detroit Tree of Heaven Woodshop, an artists' collective, to turn the wood into benches, sculptures and other features. Counting the rings showed the tree was 75 years old, and the museum hoped it would regrow from a sucker.

  In 2004, the German artist Ingo Vetter, a professor of fine arts at Umeå University in Sweden, showed a different kind of ailanthus. Influenced by the idea of the ghetto palm, he installed a living tree brought from Detroit in the exhibition Shrinking Cities at the Kunst-Werke Institute for Contemporary Art in Berlin.

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