|Foliage and immature fruit|
| Ilex opaca|
It is a medium-sized broadleaved evergreen tree growing to 10–20 m tall, exceptionally up to 30 m tall, with a trunk diameter typically up to 50 cm, exceptionally 120 cm. The bark is light gray, roughened by small warty lumps. The branchlets are stout, green at first and covered with rusty down, later smooth and brown. The winter buds are brown, short, obtuse or acute. The leaves are alternate, 5–7.5 cm long and 2–4 cm broad, stiff, yellow green and dull matte to sub-shiny above (distinctly less glossy than the otherwise fairly similar European Holly Ilex aquifolium), often pale yellow beneath; the edges are curved into several sharp, spike-like points, and a wedge-shaped base and acute apex; the midrib is prominent and depressed, the primary veins conspicuous; the petiole is short, stout, grooved, thickened at base, with a pair of minute stipules. The leaves remain on the branches for two to three years, finally falling in the spring when pushed off by growing buds.
The flowers are greenish white, small, borne in late spring in short pedunculate cymes from the axils of young leaves or scattered along the base of young branches. The calyx is small, four-lobed, imbricate in the bud, acute, margins ciliate, persistent. The corolla is white, with four petal-like lobes united at the base, obtuse, spreading, hypogynous, imbricate in bud. The flower stem is hairy with a minute bract at base. Like all hollies, it is dioecious, with separate male and female plants; only female plants produce the characteristic red berries. One male can pollenize several females. Male flowers have four stamens, inserted on the base of the corolla, alternate with its lobes; filaments awl-shaped, exserted in the sterile, much shorter in the sterile flower; anthers attached at the back, oblong, introrse, two-celled, cells opening longitudinally. The pistil on female flowers has a superior ovary, four-celled, rudimentary in staminate flowers; style wanting, stigma sessile, four-lobed; ovules one or two in each cell. The fruit is a small red drupe 6–12 mm diameter containing four seeds; it is often persistent into winter.
The species typically grows as an understory tree in forests. It is rare in the north of its range in southern Connecticut, southeastern New York, and isolated areas of Cape Cod, and always small there. It is abundant further south on the southern coast and in the Gulf states, reaching its greatest size on the bottomlands of southern Arkansas and eastern Texas. The branches are short and slender. The roots are thick and fleshy. It will grow in both dry and swampy soil, but grows slowly.
The flowers are pollinated by insects, including bees, wasps, ants, and night-flying moths. The berries are reputedly poisonous to humans, but are important survival food for birds, who will eat the berries after other food sources are exhausted. The tree also forms a thick canopy which offers protection for birds from predators and storms. Songbirds including thrushes, mockingbirds, catbirds, bluebirds and thrashers frequently feed on the berries.