Catbrier is a stout, spiny, woody perennial vine with stems that are often 4-angled, either low-climbing or extensively climbing by tendrils to a height of 25 feet.
Leaves are alternate, simple, 1½–4½ inches long, ¾–4 inches wide; heart-shaped, broadly egg-shaped, triangular, or sometimes fiddle-shaped; margins much more thickened than the rest of the leaf (see the underside); margins can be entire or set with stiff prickles; upper surface green, smooth, sometimes with white blotches, veins thickened and conspicuous in a network over the leaf surface; lower surface sometimes paler, usually with a few thorns on the midvein. The leaves are often somewhat leathery and drop off in winter.
Stems are stout canes, strongly angled, and green, with at least the older stems more or less with tufts of small, star-shaped hairs; prickles stout, green to brown or black, to ¼ inch long; tendrils arising in pairs at the base of leaf stalks. The bark is green, hard, often roughened with white scales.
Flowering is in May–June. Flowers are yellowish green, small, with male and female flower clusters on the same plant, clusters with 3–20 flowers; petals 6. The cluster’s stalk is much longer than the leaf stalk at its base.
Fruits mature September–October. Fruits are round black berries, ¼ inch thick, occurring on stalks about 1 inch long in globe-shaped clusters. Seeds usually 1 per fruit.