A climbing or trailing perennial vine with milky sap. Flowers brownish purple, like a 5-pointed star, with spreading corolla lobes ½–¾ inch long; the flower clusters arise on stalks from the leaf axils. Blooms May–June. Leaves opposite, broadly ovate and heart-shaped, to 6 inches long. Fruit a narrow pod, to 4 inches long, covered with slender, warty projections.
Similar species: Another climbing milkweed, M. baldwyniana, with whitish corolla lobes, is scattered in southwestern Missouri. Angle-pod (Gonolobus suberosus), found mostly in the Bootheel, resembles Mateliea species vegetatively but has yellowish flowers and angled (ridged) pods without warty projections. Sand vine and black swallowwort (Cynanchum spp.) have clear, not milky sap, and tiny flowers with upright, not spreading corolla lobes.