General: Planetree family (Platanaceae). Monoecious, native, deciduous trees with an open crown, among the largest of Eastern deciduous forests, reaching heights of 18-37 meters, and the greatest diameter of any temperate hardwood tree -- the largest known range 3-4 meters d.b.h.; twigs zig-zag, with only lateral buds, these completely covered by a single scale within the petiole base and not visible until after the petiole detachment; bark of upper trunk exfoliating in patches, leaving areas of inner bark exposed, a patchwork of browns, yellows, and greens against a background of white, the darker bark with age falling away in thin brittle sheets, exposing younger and lighter-colored bark. Leaves are deciduous, alternate, 10-35 cm long, palmate-veined and roughly star-shaped, with 3-5 sharp lobes, the blades often as broad or broader than they are long, truncate to cordate at the base, on petioles to 12 cm long; a leaf-like stipule at the petiole base is persistent during early growth. Staminate and pistillate flowers in separate, tightly compacted, ball-shaped clusters. Fruit is single-seeded and indehiscent (an achene), 8-9 mm long, with a ring of bristles at the base, numerous achenes in a pendulous, ball-shaped fruiting head 2-5 cm in diameter, the individual achenes drifting in the wind if the head breaks up on the tree. Common name apparently borrowed from the European sycamore maple (Acer pseudoplatanus L.), which has similar leaves. That name in turn comes from the Middle Eastern sycomore fig, Ficus sycomorus L., its specific epithet from the Greek “sykomoros,” mulberry.

Variation within the species: geographic variation in sycamore is extensive, but variants are not currently formally recognized. Platanus occidentalis var. glabrata and P. occidentalis var. attenuata are treated as synonyms of the typical expression.

The similar London planetree (below) distinguished by the lobes of its larger leaves being somewhat longer and narrower (often longer than wide), the fruiting heads 1-2 on each stalk, and the bark often somewhat greener.