4. Matelea Aubl. (climbing milkweed)

Plants with white latex and thus milky sap. Stems 1–3 m long, twining, usually climbing, branched or unbranched, moderately pubescent with spreading hairs and also minute glandular hairs (these often dark purple wherever they occur). Leaves opposite, mostly long-petiolate. Leaf blades ovate to broadly ovate or nearly circular in outline, less commonly oblong-ovate, the base deeply cordate, the tip gradually or abruptly tapered to a sharp point, the margins flat or slightly curled under, the surfaces moderately to densely pubescent with short hairs and minute glandular hairs. Inflorescences solitary in the leaf axils, mostly relatively long-stalked, consisting of sometimes branched, umbellate clusters, with 4–25 flowers. Calyces with the lobes spreading at maturity, hairy on the outer surface. Corollas more or less spreading to loosely ascending at flowering (erect in bud and sometimes after flowering), white to light cream-colored or dark purple to nearly black, hairy on the outer surface. Gynostegium appearing sessile or nearly so, the corona longer than the anther/stigma head, modified into a shallow, 5-lobed, cup-shaped crown, with narrow appendages between the lobes. Fruits pendant, lanceolate to narrowly ovate in outline, circular or slightly flattened in cross-section (not noticeably angled), the surface covered with slender, warty, hardened projections, minutely pubescent, usually with mostly glandular hairs. Seeds strongly flattened and winged, brown to dark brown, with a tuft of long, silky hairs at the tip. Two hundred to 250 species, U.S., Mexico, Central America, South America, Caribbean Islands.

Vegetatively, Missouri Matelea sometimes cannot be distinguished from Gonolobus, although in the latter genus the stems often are more sparsely hairy, and the frequency of minute glandular hairs is usually far less than in Matelea. Even species within Matelea cannot be discriminated reliably based only on vegetative characters.