Sp. Pl. 2: 999. 1753.
Trees, to 50+ m, becoming massive; trunks straight and unbranched to great heights or low-branching or multitrunked, to 4+ m diam. Leaves: stipules entire to coarsely serrate. Leaf blade light green, usually shallowly 3-5(-7)-lobed, occasionally unlobed, 6-20+ × 6-25+ cm (to 30 × 40 cm on sucker shoots), not especially thick; lobes of blade mostly wider than long, basal lobes usually smaller, often strongly reflexed, sinuses broad and gently concave, depth of distal sinuses mostly less than 1/2 distance from sinus to base of blade, terminal leaf lobe 1/2-2/3 length of blade; margins entire to coarsely serrate, teeth sometimes short-awned, apex usually acuminate; surfaces glabrate, abaxially often persistently tomentose along veins. Pistillate inflorescences: heads 1(-2); fruiting heads 25-30 mm diam.; peduncle to 15 cm. Achenes 7-10 mm, basal hairs nearly as long. 2n = 42.
Phenology: Flowering spring; fruiting late fall.
Habitat: Often abundant on alluvial soils near streams and lakes and in moist ravines, sometimes on uplands, sometimes on limestone soils, cultivated in parks and gardens and as a street tree
Elevation: 0-950 m
Ont., Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis., Mexico (Coahuila, Nuevo León, San Luis Potosí, and Tamaulipas).
Of the angiospermous trees of North America, Platanus occidentalis is one of the tallest (to 50+m) and reaches the greatest trunk diameter (to 4+m). Trees with smaller and broader-than-long leaf blades, with lobes mostly entire, have been called P. occidentalis var. glabrata (Fernald) Sargent, especially in the western range of the species from Iowa to Mexico; the range of var. glabrata overlaps that of P. rzedowskii Nixon & Peale in Tamaulipas. Trees with the blade more deeply lobed, and the base long-cuneate and decurrent on the petiole, are occasional over much of the range of the species. They have been called P. occidentalis var. attenuata Sargent.
The cultivated London plane-tree [Platanus ×acerifolia (Aiton) Willdenow, Platanus hybrida Broterius] will key here. It is distinguished by the lobes of its larger leaves being somewhat longer and narrower (often longer than wide), the fruiting heads one or two on each rachis, and the bark often somewhat greener. Many cultivars are available, some with deeper lobed or variegated leaves or with upright habit (F. S. Santamour Jr. 1986). It is often planted in cities because it is exceptionally well adapted as a street tree. Apparently it has not escaped in North America, where it is mostly seed-propagated. It is only occasionally reported as naturalized in Europe; there it is clonally propagated and is variously reported to be fertile or sterile. Reputedly, it is a hybrid of P. occidentalis with the Eurasian P. orientalis Linnaeus. Such a hybrid has been synthesized (F. S. Santamour Jr. 1972b).
Native Americans used Platanus occidentalis for a variety of medicinal purposes, including cold and cough remedies, as well as dietary, dermatological, gynecological, respiratory, and gastrointestinal aids (D. E. Moerman 1986).