Sycamore is a large tree with a massive trunk, a broad, open, irregular crown, and large, crooked, spreading, white branches.
Leaves are alternate, simple, 4–8 inches long and broad or larger; with 3–5 broad, shallow lobes with coarse teeth, each lobe tip pointed; upper surface bright green; lower surface whitish, hairy; leaf stalk hairy, with a leafy appendage at the base.
Bark is very distinctive: smooth, greenish on young trunks, turning reddish-brown to gray; bark sheds in thin plates to reveal the distinctive white new bark.
Twigs are slender, shiny, zigzag; buds are entirely enclosed by the base of the leaf stalk.
Flowers April–June; male and female flowers on the same tree with numerous flowers in globe-shaped clusters. Male flower cluster red or yellow, about 3/8 inch in diameter; female flower cluster red, about 1/2 inch in diameter, occurring singly.
Fruits September–October, persist through winter, solitary, rounded, dry, 1–1½ inches wide, drooping on a stalk 3–6 inches long; ball composed of many closely packed, long, narrow fruits.
Similar species: This is Missouri's only native sycamore. The London plane tree (P. xacerifolia) is a hybrid with an Asian sycamore species, and it has existed since the 1600s. You can identify it by the deeper sinuses in its leaves and by its fruiting balls that occur in pairs (not singly). It tolerates pollution and rootball compaction, and it has long been a popular street tree in North America and Europe. The trees that line the glamorous Champs-Elysées boulevard in Paris, France, are London plane trees that have been pollarded (a particular, careful kind of pruning). In Missouri, you may encounter London plane trees in cultivation (along streets, on college campuses, in parks, and so on).
There are about 10 sycamore species worldwide, including two in the the western United States: if you travel to California, you may see the California sycamore (P. racemosa); if you visit Arizona or New Mexico, the native species is the Arizona sycamore (P. wrightii). Five other sycamore species occur on our continent, south of the US border in Mexico.