American basswood is a medium-sized tree with small, horizontal, often drooping branches forming a broad, rounded head.
Leaves are alternate, simple, 5–6 inches long, 3–5 inches wide, broadest near the base; margin coarsely toothed; tip pointed, base unequal, rounded; upper surface dark green, shiny; lower surface paler, with tufts of hair in the vein axils.
Bark is light brown to gray, with deep furrows and narrow, flat-topped, long ridges that shed small, thin scales. Often with sprouts around the base of older trees.
Twigs are slender, smooth, green to brown turning gray with age; pores numerous; winter buds dark red, egg-shaped, ¼ inch long.
Blooms late May–July; 6–15 flowers on a drooping, slender, smooth stalk; stalk attached to a strap-shaped, reduced leaf, 2–5 inches long, ¾-1½ inches wide, smooth, strongly veined; flowers pale yellow to whitish, fragrant, ½ inch in diameter.
Fruits August–October; dry, persistent, nearly round, ¼ inch long, covered with dense brown hairs.
Similar species: White basswood (T. heterophylla) has a more limited distribution in Missouri, occurring mainly along rocky woods and bluffs bordering streams. Its leaves are densely but not coarsely toothed, and the lower surfaces are covered with white or brown matted, woolly hairs.