Baldwyn’s or climbing milkweed, Baldwyn’s spinypod

Gonolobus baldwinianus Sweet, Hort. Brit. ed. 2, 360. 1830; Odontostephana baldwyniana (Sweet) Alexander

Vines, herbaceous. Stems 1(–3), twining, 100–200 cm, hir­sute with eglandular and incon­spicuous glandular trichomes. Leaves with 0–2 colleters on each side of petiole; petiole 2–5 cm, hirsute with eglandular and inconspicuous glandular trichomes; blade ovate to oval (orbiculate), 3–17 × 2–15 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 or paired, simple to compound umbelliform, extra-axillary, pedunculate, 4–20-flowered; peduncle 1–9.5 cm, hirsute with eglandular and inconspicuous glandular trichomes. Pedicels 3–15 mm, hirsute with eglandular and inconspicuous glandular trichomes. Flowers: calyx lobes spreading, elliptic, 1.9–3.2 mm, apex acute, hirsute with eglandular and inconspicuous glandular trichomes; corolla white to cream, not or faintly reticulate, campanulate, tube 0.5–2 mm, lobes erect (spreading), twisted, oblong to narrowly deltate to narrowly obovate, 5–9 mm, hirtellous abaxially, glabrous adaxially; corona of 5 united lobes with lateral, subulate lobes at apex greatly exceeding medial lobe, adaxial appendages incurved, incumbent on anthers, often concealed by erect corolla lobes, white or cream to yellow (purple), 1.5–2.5 mm, glabrous; apical anther appendages cream, green at base, truncate; style apex green, rounded-pentagonal, convex. Follicles not striate, lance-ovoid, 9–12 × 1.7–2.5 cm, moderately muricate, minutely short-hirsute. Seeds brown, oval to ovate, 7–9 × 5–7 mm, margins broadly winged, chalazal end entire, faces rugose; coma 2–4 cm.

Flowering Apr–Jul; fruiting (May–)Jun–Oct(–Dec). Rocky, clay (rarely sandy) soils, limestone, shale, dolomite, hill slopes, valleys, bluffs, riparian, pine, and mixed-hardwood forests, oak-hickory woods, glades, shady meadows; 30–500 m; Ala., Ark., Fla., Mo., Okla., Tex.

Matelea baldwyniana is most common in the south­western portion of the Ozark uplift, from southwestern Missouri to southeastern Oklahoma. A single location in northern Texas on the Oklahoma border, on the shores of Lake Texoma (an impoundment of the Red River), is disjunct by 100 km from the nearest popu­lation in the Ouachita Mountains, and is docu­mented only by a photograph. Furthermore, the flowers on this plant are unusual, with pinkish tinged corollas and maroon coronas unknown from other populations of M. baldwyniana. It is possible that this population represents a pale-flowered variant of M. decipiens. Matelea baldwyniana has a well-documented disjunc­tion of 600 km across the Mississippi Valley to south­western Alabama, where populations extend along the Gulf Coastal Plain to the Florida Panhandle. The species is uncommon in the southeastern portion of the range, where it is considered to be of conservation concern in both Alabama (Clarke, Monroe, and Wilcox counties) and Florida (Gadsden and Jackson counties). The species is not known to occur in Georgia; however, it has been reported from the state based on uncertainty regarding typification (M. Fishbein and A. McDonnell, unpubl.). The cream corollas with ascending, twisted lobes are unique among the Matelea species in the flora area but recall those of Polystemma cordifolium, a species just entering the flora area in extreme southern Arizona.