Tree-of-Heaven (Ailanthus altissima), also knows as Ailanthus and Chinese Sumac, a native of China, was first imported to Europe in the 1740's and subsequently was widely planted in many European cities. It was brought to the US in the 1780's and was planted as a street tree in many eastern cities because it is tolerant of smoke and soot and can thrive in poor soils. It gradually became naturalized and spread throughout much of North America. It is considered to be invasive in at least 30 states, including Tennessee where it is ranked as a 'Severe Threat' by the Tennessee Exotic Pest Plant Council. Tree-of-Heaven has alternate, very large (1-3 ft long), pinnately compound leaves with leaflets that have one or more glandular teeth near the base and no other teeth along their margins - a feature that distinguishes it from species of Sumac, Ash, and Black Walnut, all of which have teeth around the entire leaflet margins. This tree grows rapidly and reaches heights of 80-100 ft. It is dioecious, with small, pale yellow to greenish male and female flowers usually being borne on separate trees. It produces large numbers of flat, twisted, winged fruits, each with a single central seed. Its prolific production of seeds and its ability to sprout readily from roots after being cut back account for its invasive character. In addition, it is reported to produce toxic chemicals that inhibit the growth of other plants in its immediate vicinity.