Medium-sized to large tree 16 - 24 m tall, trunk diameter 0.5 - 1 m Leaves: alternate, on long, densely hairy leafstalks, dark green above, white-hairy beneath (becoming hairless), 5 - 10 cm long, nearly as wide, egg-shaped (leaves in upper crown may be palmate, with three to five lobes) with a straight or slightly heart-shaped base and bluntly pointed tip, broadly toothed. In autumn the leaves turn yellow. Flowers: either male or female, borne on separate trees (dioecious) in hairy-bracted catkins. Male catkin 4 - 8 cm long, cylindrical, and thick. Anthers purple. Female catkin 2 - 5 cm long and slender. Stigmas yellow. Fruit: a two-valved capsule, borne in 4 - 8 cm long drooping catkins, greenish, flask-shaped, often curved, and hairy. Seeds light brown with cottony hairs attached. Bark: whitish or gray, thin, smooth or with diamond-shaped indentations (lenticels) on young trees, becoming dark gray to black, thick, and deeply fissured at the base. Twigs: stout, green, and hairy when young, becoming greenish gray or pale brown with dark blotches. Leaf scars crescent-shaped with 3 bundle scars each. Buds: reddish brown, 3 - 6 mm long, egg-shaped, pointed, and hairy. Form: broadly rounded or irregular, with a crooked and often forked trunk.
Similar species: The similar Populus balsamifera and P. heterophylla differ by having flattened leafstalks. The hybrid Populus x canescens (of which P. alba is a parent) is very similar in appearance but its smaller, toothed leaves do not form lobes.
Flowering: late March to late April, before the leaves
Habitat and ecology: Introduced from Eurasia. Often found along roads, around old homesites, and in degraded woodlands. Frequently planted and escaping from cultivation. By means of suckers, forms large vegetative colonies that are hard to eradicate. These colonies are not technically considered part of the flora, since the "parent" tree was probably planted.
Occurence in the Chicago region: non-native
Notes: Planted as an ornamental due to its silvery leaves. Populus species as a whole, however, are subject to many diseases and insect pests, such as canker and tent caterpillars, which often kill the tree or make it unattractive. These risks, in conjunction with a water-hungry root system, have made Populus species less desirable for landscape use.
Etymology: Populus is the Latin word for poplar. Alba means white.
Trees with whitish-gray bark and mostly widely spreading branches; terminal bud and young twigs tomentose; lvs white-tomentose beneath, palmately 3-7-lobed on long shoots, ovate and irregularly dentate on short ones; stamens 6-10; stigmas 2, bifid, filiform; fr narrowly ovoid, the pedicel 1-2 mm; seeds (1)2(3) per placenta; 2n=38, 57. Native of Eurasia, commonly planted, and occasionally escaped. A columnar form is cv. Bolleana' (P. bolleana)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.