Yellow Carolina milkvine, yellow-flowered or Carolina yellow spinypod

Gonolobus flavidulus Chapman, Bot. Gaz. 3: 12. 1878; Odontostephana flavidula (Chapman) Alexander

Vines, herbaceous. Stems 1, twining, 100–200 cm, hir­sute with eglandular and incon­spicuous glandular trichomes. Leaves with 2 colleters on each side of petiole; petiole 1–6 cm, hirsute with eglandular and inconspicuous glandular trichomes; blade ovate (orbiculate), 5–15 × 2–10 cm, base shallowly to deeply cordate, with (2–)4 laminar colleters, apex acute to acuminate, surfaces hirsute with eglandular and inconspicuous glandular trichomes. Inflorescences solitary, umbelliform, extra-axillary, pedunculate, 3–20-flowered; peduncle 0.5–4.5 cm, hirsute with eglandular and inconspicuous glandular trichomes. Pedicels 3–20 mm, hirsute with eglandular and inconspicuous glandular trichomes. Flowers: calyx lobes spreading, deltate to elliptic, 1.4–2.4 mm, apex acute, hirsute with eglandular and inconspicuous glandular trichomes; corolla pale yellow to green abaxially (maroon or maroon tinged), pale green to yellow-green (maroon or maroon tinged), with a cream to yellow ring at base of corona adaxially, frequently with green reticulations visible on both sides, rotate, tube 1–1.5 mm, lobes spreading, elliptic or oblong to oblanceolate, 4.5–11 mm, margins plane to slightly reflexed, minutely hirtellous abaxially, glabrous adaxially; corona united to column near base, of 5 segments, united in basal one-half, fleshy, each with small lateral lobes at apex, exceeded by medial lobe, forming a sheath that equals (exceeds) style apex, adaxial appendages incurved, incumbent on anthers, yellow to orange-yellow (maroon), 1.5 mm, glabrous; apical anther appendages bright white with green patch at base, truncate, covering less than 25% of style apex; style apex green, pentagonal, flat. Follicles not striate, lance-ovoid to ellipsoid, 8–15 × 1.5–2.5 cm, apex acuminate, muricate, sparsely and minutely hirsute to glabrous. Seeds dark brown, ovate (orbicular), 7–9 × 5–7 mm, margins broadly winged, chalazal end entire, faces rugose; coma 1.5–2.5 cm.

Flowering Apr–Jul; fruiting Jul–Oct. Sandy and calcareous substrates, hillsides, bluffs, and stream banks, hardwood and pine-hardwood forests; 0–300 m; Fla., Ga., S.C.

Matelea flavidula is uncommon on the Atlantic and Gulf coastal plains in Florida (Gadsden County), Georgia (Baker, Colquitt, Cook, and Decatur counties), and South Carolina (Charleston, Clarendon, and Georgetown counties). It is highly localized in Gadsden County, Florida, where its range contacts that of M. alabamensis, and it is considered to be endangered in that state. Reports from Alabama appear to be based on yellow-flowered plants of M. carolinensis. Although uncommon, its global status has not received much attention, and a current assessment is needed, patricularly since misidentification of specimens may have contributed to an overestimation of the number of extant populations. The narrower lobes of the yellow-green reticulate corollas and taller corona, along with more sparsely muricate follicles, distinguish M. flavidula from M. alabamensis.