Smilax rotundifolia, roundleaf greenbrier, is a perennial woody vine native to the eastern and southeastern United States and southern Canada. In Pennsylvania it grows in a wide range of habitats, including moist to dry forests, woodlands, thickets, hedgerows, fields, and pond borders. This thorn‑armed vine climbs up surrounding vegetation or forms dense, tangled ground masses. Climbing is aided by green tendrils that arise from the bases of the petioles. Stems are round with faint angles, green to woody with age, and bear scattered prickles.

Prickles measure 2–6 mm long, pale with darker tips, and are not present on every stem. Leaves are alternate, rounded to broadly ovate, smooth, 1½–5" long, with smooth margins. The upper surface is glossy dark green; the lower surface is paler. Leaf stalks are ¼–½" long, light green, and smooth, with a pair of tendrils at the base.

Roundleaf greenbriar is dioecious, with male and female flowers on separate plants. Flowers are yellow-green to greenish to white-greenish and small, typically ⅛–¼" (3–6 mm) long. Each flower has six green to greenish-white tepals, free or slightly united at the base. Male flowers bear six stamens with pale anthers, while female flowers contain a single pistil with three short, spreading stigmas. Flowers are arranged in axillary umbels of 3–15 (occasionally up to 20) blossoms, each umbel borne on a slender stalk arising from the leaf axils. This species blooms May to mid-June in Pennsylvania.

After fertilization, the female flowers develop into bluish‑black berries with a pale, whitish bloom. The fruits are about ¼" across, round, and contain 1–3 seeds. Berries often persist into late winter and provide food for northern cardinals, white‑throated sparrows, and other fruit‑eating birds.

The foliage is browsed by white‑tailed deer and rabbits, and serves as host material for several insects, including the Smilax leaf beetle, Smilax leaf midge, woolly maple aphid, Smilax stem gall wasp, the caterpillar of the false diamondback moth, and the Smilax leafminer moth. The flowers are pollinated by small bees, flies, and butterflies.

Roundleaf greenbriar reproduces both vegetatively and by seed. It spreads vigorously by lateral underground rhizomes, which send up new shoots that climb or sprawl to form dense, clonal thickets. This rhizomatous growth allows the species to expand rapidly across suitable habitat. Sexual reproduction occurs through the seeds contained in the berries. The fruits are eaten primarily by birds, which disperse the seeds to new locations, with occasional dispersal by mammals.

The young shoots, leaves, and tendrils of Smilax rotundifolia are edible. The tender spring shoots can be cooked and eaten much like asparagus, while the young leaves and tendrils can be prepared as mild greens or added raw to salads when very young.