1. Gonolobus suberosus (L.) W.T. Aiton

Matelea suberosa (L.) Shinners

G. gonocarpus (Walter) L.M. Perry

M. gonocarpa (Walter) Shinners

Pl. 223 j–l; Map 934

Plants with milky latex and thus white sap. Stems 1–3(–6) m long, twining, usually climbing, branched or unbranched, sparsely to moderately pubescent with spreading hairs, usually also with sparse to moderate, minute glandular hairs. Leaves opposite, mostly long-petiolate. Leaf blades 4–20 cm long, oblong-ovate to triangular-ovate or broadly ovate, the base deeply cordate, the tip abruptly or gradually tapered to a sharp point, the margins flat, sparsely short-hairy along the veins, usually also with sparse to moderate, minute glandular hairs. Inflorescences solitary in the leaf axils, sessile to long-stalked, consisting of sometimes branched, umbellate clusters with 2–25 flowers. Calyces with the lobes 2.5–6.0 mm long, spreading at maturity, narrowly triangular to narrowly lanceolate, glabrous except for sparse, short hairs along the margins toward the tip. Corollas with the lobes 7–15 mm long, strongly spreading at flowering, narrowly lanceolate, yellow to yellowish green, glabrous. Gynostegium appearing sessile or nearly so, the corona present as a flattened, fleshy, irregularly 5-angled disk shorter than the anther/stigma head, yellow to orangish brown. Fruits 7–15 cm long, pendant, lanceolate to narrowly ovate in outline, sharply 5-angled in cross-section, the surface smooth, glabrous. Seeds with the body 6–10 mm long, elliptic-obovate in outline, strongly flattened and with a narrow to relatively broad, irregularly toothed wing, dark brown, with a tuft of long, white, silky hairs at the tip. June–August.

Uncommon in southern Missouri, mostly in the Mississippi Lowlands Division (southeastern U.S. west to Kansas and Texas). Swamps, bottomland forests, lower ledges of bluffs, margins of lakes and sloughs, and banks of streams and rivers; also disturbed wooded areas.

The nomenclature and taxonomy of this species complex are relatively complicated. The present treatment follows that of Lipow and Wyatt (1998), who summarized problems of nomenclature and typification in the introduction to their study on the reproductive biology and breeding system of the species. Drapalik (1970) presented evidence that G. gonocarpus and G. suberosus should be treated as part of a single variable species, based on his observation of specimens intermediate between the two traditionally accepted taxa. Reveal and Barrie (1992) studied lectotypification (designation of an official type specimen) of the epithet suberosus and concluded that it has priority over gonocarpus if the two names are considered to represent a single species. More recently, Krings and Xiang (2004) concluded that the two taxa are more or less distinguishable in the complex, but they emphasized different floral characters to separate the two than those used by most earlier authors. Although Krings and Xiang did not recommend a particular taxonomic disposition of their two entities, they suggested that if two are to be recognized as specifically distinct, then the western taxon (including Missouri) with glabrous, concolorous corollas should probably be called G. granulatus Scheele.