Shortcrown milkvine

Gonolobus parviflorus (Torrey) A. Gray [not Decaisne] var. brevicoronatus B. L. Robinson, Proc. Amer. Acad. Arts 26: 169. 1891; Vincetoxicum brevicoronatum (B. L. Robinson) Vail

Herbs. Stems 5–20, prostrate, often branched near base, 10–40 cm, hirsute with long eglandular and minute glandular trichomes. Leaves with 1 or 2 colleters on each side of petiole; petiole 0.2–0.9 cm, hirsute with long eglandular and minute glandular trichomes; blade ovate to deltate (lanceolate or orbiculate), 1.1–2.9 × 0.5–2.3 cm, base rounded or truncate (cordate), laminar colleters appar­ently absent, apex acute to acuminate, surfaces hirsute with long eglandular and minute glandular trichomes, especially so on veins abaxially. Inflorescences solitary, simple or compound umbelliform, extra-axillary, pedun­culate, 2–8-flowered; peduncle 1.2–7.3 cm, hirsute with long eglandular and minute glandular trichomes. Pedicels 2–6 mm, hirsute with long eglandular and minute glandular trichomes. Flowers: calyx lobes erect, elliptic, 1.5–2.5 mm, apex acute, hirsute with long eglandular and minute glandular trichomes; corolla green, faintly to strongly reticulate, campanulate, tube 1–2 mm, lobes spreading to erect, planar, deltate, 1–3 mm, glabrous adaxially; corona united to corolla and column near base, composed of 2 series, the outer of 5 laminar segments shorter than the style apex, apical margins unlobed, the inner of 5 subulate segments inflexed over the style apex, green or yellow, 0.7–1 mm, glabrous; apical anther appendages white, green at base, deltoid; style apex rounded-conic. Follicles not striate, lance-ovoid, 3–6.5 × 1.5–3 cm, apex acute, densely muricate, hirsute. Seeds tan to light brown, ovate, 10–11 × 7–8 mm, margins broadly winged, chalazal end erose, faces minutely rugose; coma 2–2.5 cm.

Flowering Feb–Jul; fruiting Mar–Sep. Sandy sub­strates, flood plains, thornscrub; 100–200 m; Tex.

Matelea brevicoronata is uncommon and localized in southern Texas in the vicinity of Laredo (Webb and Zapata counties), on alluvial sands overlying sandstone. Its range is far more restricted than previously thought because variants of M. parviflora (as treated here) with short coronas were included in a broader concept of M. brevicoronata. These species are nearly identical in vegetative characters, and are distinguished only by a combination of floral characters. Compared to M. parviflora, the corollas of M. brevicoronata are campanulate with spreading to ascending lobes that are glabrous adaxially or obscurely hirtellous at the base (versus rotate with spreading to reflexed lobes that are sometimes densely hirtellous adaxially, especially when the lobes are spreading and approaching the orientation of M. brevicoronata). Additionally, the inner corona segments of M. brevicoronata are inflexed over the style apex (versus erect to spreading), and the outer segments lack marginal lobes at the apex (versus minute to more commonly elongate lobes, giving the combined corona segments the appearance of a trident). So far as known, the ranges of the two species approach each other but do not overlap. Because of the highly restricted dis­tribution documented by fewer than ten collections, M. brevicoronata should be considered to be of extreme conservation concern.