Populus L.
Family: Salicaceae
Aspen, Cottonwood, Poplar
Populus image

Key to Wisconsin Populus

Author: John G. Zaborsky

    • 1a.Mature leaf blades with abaxial surfaces densely tomentose with white hairs; leaves of long shoots palmately lobed P. alba

    • 1b.Mature leaf blades with abaxial surfaces glabrous or nearly so (tomentose when young in P. grandidentata); leaves of long shoots merely toothed, not lobed 2

    • 2b.Petioles flattened 3

    • 3a.Leaf blades broadly triangular or diamond-shaped, the margins with a firm, translucent border; stamens 15+; floral bracts glabrous 4

    • 3b.Leaf blades orbicular to reniform, or obscurely triangular, the margins without a firm, translucent border or with one no thicker than adjacent main veinlets; stamens 12 or fewer; floral bracts pilose 5

    • 4a.Glands present at the base of the blade; blades broadly triangular, the margins minutely ciliate (at least on the teeth) P. deltoides

    • 4b.Glands absent at the base of the blade; blades diamond-shaped, the margins glabrous P. nigra

    • 5a.Leaf margins coarsely serrate with 10 (–12) or fewer teeth per side (except on vigorous young sprouts); buds and new growth pilose or tomentose P. grandidentata

    • 5b.Leaf margins subentire to finely crenate-serrate with 15 or more teeth on a side; buds and new growth glabrous or nearly so P. tremuloides

Our native aspens and poplars can form extensive groves via underground suckers and a large stand of trees may represent a single individual plant. Leaves are variable in our species, but typical material is readily identified. Wisconsin taxa can form numerous hybrids, some of which have been collected in the state; they are accounted for in the species descriptions.