Herbs. Stems annual, erect, unbranched, 0.5–1 m, herbaceous; prickles absent. Leaves numerous, evenly distributed, larger distally; petiole thin, equaling or longer than blade; tendrils distal, few, short; blade narrowly ovate, pubescent and not glaucous abaxially, base rounded to truncate, margins convex, apex acute to acuminate. Umbels 3–10, axillary to leaves and bracts, 10–50-flowered, semiglobose; proximalmost peduncle longer than distalmost. Flowers: tepals 3.5–4.5 mm; anthers usually shorter than filaments; ovules (1–)2 per locule. Berries blue to black, globose. 2n = 26.

Flowering May--Jun. Roadside thickets, woods; 150--600 m; Ont.; Ill., Ind., Iowa, Mich., Minn., Mo., Ohio, Wis.

Smilax illinoensis is intermediate between S. ecirrhata and S. lasioneura.