Poplar, a hardy tree of the north temperate zone, related to the willow. Of the 35 species, 15 are native to North America. Certain species are called aspen and cottonwood. Popple is a colloquial word for poplar and also for aspen wood. Poplars often are cultivated as shade trees and windbreaks. Poplar wood is very soft, and is used chiefly for paper pulp, boxes and crates, and matches. The bark is used in tanning.
Poplars are quick-growing, short-lived trees found mainly along streams. Most species are fairly tall, with a rounded or columnar shape. The leaves, arranged alternately on the stems, may be oval, lance-like, or heart-shaped, and have long stalks and toothed margins. Poplar leaves turn yellow in autumn.
Poplars have tiny flowers, without petals or sepals, that form long, hanging clusters called catkins. Male and female flowers are borne on separate trees. The fruits are small pods that ripen before the leaves are fully grown. In several species the pods release seeds attached to silky threads—the “cotton” that blows from the trees in early spring.
Cultivated poplars are propagated by cuttings. The trees grow best in wet soil. The shallow, spreading roots are troublesome near gardens and sidewalks. Poplars are subject to canker diseases, galls, root rot, and rusts.
Native North American poplars grow about 90 feet (27 m) tall. The balsam poplar, or tacamahac, of eastern North America has six-inch (15-cm) leaves that are somewhat rounded at the base. The eastern cottonwood has heart-shaped leaves. The plains cottonwood has similar leaves but has a spreading, irregular crown. The narrowleaf cottonwood of western North America has nearly willowlike leaves. The quaking aspen, a tree of northern regions, has sparse foliage of trembling, nearly round leaves. (The leaves of certain poplars tremble, or quake, because the leafstalks are flattened, and bend in the slightest breeze.) The bigtooth aspen, an eastern species, is a small tree named for its coarsely toothed leaves.
Introduced species include the black poplar of Europe, 40 to 90 feet (12–27 m) tall, with a spreading crown. The trembling leaves, about four inches (10 cm) long, are triangular or wedge-shaped. The Lombardy poplar is a columnar variety of the black poplar. The white, or silver-leaved, poplar, also from Europe, is 30 to 70 feet (9–21 m) tall and has lobed leaves that are white beneath. The bolleana poplar, a variety of the white poplar, is shaped like the Lombardy poplar.
Hybrid poplars include the Carolina poplar, which may be derived from the black poplar and balsam poplar. It is a pyramid-shaped tree, 40 to 100 feet (12–30 m) tall, with triangular, trembling leaves. Balm of Gilead is a poplar of unknown, possibly hybrid, origin.
The tulip tree is sometimes called yellow poplar, tulip poplar, or hickory poplar. It does not belong to the same genus as true poplars.
The balsam poplar is Populus balsamifera; black, P. nigra; Lombardy, P. n. italica; white, P. alba; Bolleana, P. a. bolleana; Carolina, P. canadensis; eastern cottonwood, P. deltoides; plains, P. sargentii; narrowleaf, P. angustifolia; quaking aspen, P. tremuloides; bigtooth, P. grandidentata; balm of Gilead, P. candicans. All belong to the willow family, Salicaceae.