Flower:

Showy, loose to dense, semi-pyramidal branching clusters 4 to 6 inches long at branch tips. Flowers are intermixed staminate (male), pistillate (female) and perfect (both male and female parts), about 1 inch across with 4 pale yellow to greenish-yellowish petals. The upper petals are erect, oblong to spatula-shaped with fringed edges and an orange-red stripe down middle; lateral petals are egg-shaped, cupped forward with fringed edges. The 7 stamens are longer than the petals, flaring out and up from the center, white with deep orange tips (anthers). The single style is longer than stamens, white with an obscure stigma at the tip, extended down and out below the stamens. The calyx cupping the flower is bell shaped with 5 lobes, ¼ to 1/3 as long as the petals. Flower and cluster stalks are hairy.

Leaves and bark:

Leaves are opposite, long stalked, palmately compound with 5 to 7 leaflets. Leaves at branch tips can be tightly clustered nearly appearing whorled. Leaflets are 2½ to 6¼ inches long, ¼ to 2½ inches wide, generally elliptic, finely toothed around the edges, widest at or above middle, with a long or short taper to a pointed tip, and tapering at the base. The upper surface is hairless, bright green, the lower paler in color with conspicuous tufts of hair in vein axils. Fall color is gold to red-orange.

Branches and twigs are stout, especially on full sun specimens. Terminal buds very large, ½+ inch long, smaller below, egg shaped with a pointed tip. Bud scales are also egg-shaped with pointed tips, dull, light brown colored, and the tip edge slightly spreading. Leaf scars are broadly to narrowly smiley faced with three conspicuous vascular bundle scars. Bark a dull brownish gray due to very fine soft hairs, with scattered pale lenticels (pores), turning darker and smoother, though developing scaley patches with age.

Branch bark becomes rough with a shallow, wrinkly gray-brown ridge pattern; older bark is rough with shallow longitudal ridges. Trunks are typically 10 to 16 inches diameter max in Minnesota, but up to 24 inches in its native range.

Fruit:

Fruit is a fleshy, globular capsule, 1½ to 2 inches diameter, golden brown, the surface leathery and covered in short spines, though may be just bumpy rather than spiny.

Each capsule contains 1 to 3 nuts that are large, shiny, dark reddish-brown with a large, pale, circular "eye".

Notes:

Minnesota sits just northwest of Ohio Buckeye's native US range, where it is typically a mid-sized understory woodland species. Grown in the open it can attain a massive size of up to 75 feet and trunk girth of 2 feet. In Minnesota it's a fairly common tree in urban and rural landscapes, though typically grown in the open it rarely gets much taller than 40 feet, with a trunk diameter of 12 to 16 inches. It has only twice been documented as naturalized though it is likely widely under noted by field botanists. Squirrels love the nut, burying it widely and volunteer saplings are typically common in lawn edges, gardens and woodline edges near a parent tree. Considered by some as a "messy" tree due to the copious amounts of fallen nuts and husks, the tree itself is rather beautiful when in full flower. Squirrels typically take all the nuts leaving only discarded shells and husks to be raked up. While it can develop deep gold to red-orange fall color, it is commonly susceptible to foliar leaf spot diseases and leaf scorch causing premature leaf drop by late summer, especially in hot, sunny locations.

Ohio Buckeye resembles the related Horse Chestnut (Aesculus hippocastanum), which is native to the Balkans of southeast Europe and also planted in landscapes in the US, occasionally escaping cultivation the same as Ohio Buckeye. Horse Chestnut has white flowers and leaflets are all typically widest near the tip with an abrupt taper to a short point, where Ohio Buckeye has pale yellow flowers and leaflets have a longer taper at the tip. Horse Chestnut buds are also up to 1½ inches long, rather shiny and sticky with 6 to 8 vascular bundles in the leaf scar, where Ohio Buckeye buds are about ½ inch long, dull and smooth and have 3 bundles in leaf scars.