Tree 9 - 15 m tall, 20 - 38 cm in diameter Leaves: opposite, palmately compound, stalked, with five (rarely seven) leaflets. Flowers: either male, female or bisexual on the same plant (poygamomonoecious), borne on a loosely branched inflorescence (panicle), yellow, 12 - 15 cm long, 5 - 7 cm wide, with four hairy petals and stamens that are much longer than the petals. Fruit: a prickly, leathery capsule enclosing a single seed. The seed is 2 - 3 cm in diameter and shiny brown with a pale circular marking. Bark: yellowish brown and smooth to scaly when young, becoming furrowed with short ridges or plates. Twigs: reddish brown changing to gray, smooth. Terminal buds: 1.5 - 1.8 cm long, egg-shaped, not sticky, with brown outer scales and yellowish green inner scales. Leaflets: yellowish green above, paler beneath, 7 - 15 cm long, 3 - 6 cm wide, elliptic or inversely egg-shaped and tapering at both ends, finely toothed. Leaves turn yellow in fall. Odor: unpleasant, released from most plant parts when crushed.
Similar species: Aesculus hippocastanum usually has seven to nine leaflets, sticky terminal buds 2 - 4 cm long, 5 cm diameter fruit, and lacks an unpleasant odor.
Flowering: Late April to mid May
Habitat and ecology: Wet mesic woods, bottomland forests, rich woods, and floodplains.
Occurence in the Chicago region: native
Notes: Seeds of this species are poisonous to humans and livestock but are edible for the fox squirrel. Hummingbirds are attracted by the flowers. According to an old superstition, carrying the nut in a pocket protects against rheumatism.
Etymology: Aesculus is the Latin word for a species of oak with edible nuts, but was used by Linnaeus to name this genus. Glabra comes from the Latin word meaning "smooth" or "lacking hairs."
Small tree to 15 m; lfls 5(-7), bright or yellowish-green, oblanceolate to obovate, 6-16 נ3-6 cm, acute or acuminate, serrate, with conspicuous tufts of hair in the vein-axils beneath; infls 1-1.5 dm; cal 5-8 mm; pet 4, greenish-yellow, 1-2 cm, the 2 uppermost oblanceolate, slightly exceeding the 2 lateral, gradually tapering to the claw, the lateral with elliptic-oblong to elliptic-ovate blade and slender claw; stamens 7, often twice as long as the cor; fr generally echinate, 3-4 cm thick; 2n=40. Moist but fairly well drained, chiefly alluvial, often calcareous soil; w. Pa. to s. Ont., s. Wis., Io., and Kans., s. to Tenn., n. Ala., Ark., and Tex. Apr., May. Our plants, as here described, are var. glabra.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Diagnostic Traits: Twigs rank when broken; leaves opposite, palmately compound, leaflets usually 5, margins finely serrate; winter buds not sticky; flowers yellowish; fruits a leathery, somewhat spiny capsule with 1 or 2 large, lustrous brown seeds.
Deam (1932): The fruit is poisonout to stock, although it rarely proves fatal. In our area the buckeye is the first tree to put out its leaves. On this account in early spring it can be distinguished easily in the forest. This character together with its large clusters of flowers which appear early are features which recommend it for shade tree and ornamental planting.