Ailanthus is a very high pollen producer. This tree has been a moderate source of allergy in the U.S.
The leaves of tree of heaven are 12-24 inches long, broadly lance shaped, and covered with fine hairs when young. The tree can grow to 50 feet tall. Bark is light brown and smooth. Flowers are 1/4 inches long, greenish-yellow in color. The fruit is 1 1/2 inches long, showy, reddish-green in color. Tree of heaven is native to China and has naturalized throughout much of the U.S. It is generally planted in urban areas. This tree is said to be the tree in the classic novel A Tree Grows in Brooklyn, by Betty Smith.
The tree of heaven has pollen grains that are prolate to subprolate; the amb subtriangular and 3-colporate. The colpi are long and narrow with tapering ends. The sexine is reticulate and the intine is thickened below the apertures.
The grains measure 28-34 x 20-21 micrometers.
The shaded areas on the map indicates where the genus has been observed in the United States.
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