American holly is a small- to medium-sized evergreen tree or shrub, with short, crooked branches and a rounded or pyramidal crown.
Leaves are alternate, simple, thick, leathery, elliptical, 1½ to 3 inches long; wavy-edged with large, sharp, spine-tipped teeth; upper surface dark green, dull, smooth; lower surface paler green, smooth to somewhat hairy.
Bark is thin, brown to grayish-brown, with warty projections.
Twigs are stout, green to light brown or gray, covered with fine, rust-colored hairs when young, smooth later; pores small.
Flowers May–June, in short-stalked clusters, male and female flowers on separate plants or sometimes on the same plant; petals 4, white. Male flowers in clusters of 3–9; female flowers single or in groups of 2–3.
Fruits in October; bright red-orange berries, ¼ inch in diameter; often remaining on tree over winter.
Similar species: Four species of hollies (genus Ilex) can grow without cultivation in Missouri's wild habitats. American holly is the only one with the leaf blades tipped with a spine and the margins of the leaf blades usually also with spine-tipped teeth. Our other hollies lack spines on the leaves. Our other two native hollies are possum haw or deciduous holly (I. decidua), whose relatively thin leaves drop off in winter, and winterberry or black alder (I. verticillata), whose leaves are saw-toothed but not spine-tipped. Yaupon (I. vomitoria), our fourth hollly, is occasionally cultivated here as an ornamental shrub, and it has been collected only once in Missouri, growing wild along a railroad — in 1897.