Smallflower milkvine

Lachnostoma parviflorum Torrey in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 165. 1859; Vincetoxicum parviflorum (Torrey) A. Heller

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), 0.5–4 × 0.3–3 cm, base rounded or truncate to cordate, with 0–4 laminar colleters, apex acute to acuminate, surfaces hirsute with long eglandular and minute glandular trichomes, especially so on veins abaxially. Inflorescences solitary, compound racemiform, extra-axillary, pedunculate, 2–20-flowered; peduncle 0.7–10 cm, hirsute with long eglandular and minute glandular trichomes. Pedicels 1–10 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 to purple, faintly to strongly reticulate, rotate, lobes spreading to reflexed, planar, ovate, lanceolate, or oblong, 1–4 mm, hirtellous adaxially at base of lobes or rarely throughout; corona united to corolla and staminal column near base, composed of 2 series, the outer of 5 laminar segments shorter than the style apex, apical margins with minute to elongate lateral lobes, the inner of 5 erect, subulate segments exceeding the style apex, white or greenish cream, 0.8–3 mm, glabrous; style apex rounded-pentagonal, flat. Follicles not striate, ovoid to ellipsoid, 6–10.5 × 1.5–3 cm, apex acuminate, moderately to densely muricate, hirsute. Seeds tan to light brown, broadly ovate to nearly orbicular, 10–16 × 9–15 mm, margins broadly winged, chalazal end minutely erose, faces minutely rugose; coma 2–4 cm.

Flowering Mar–Oct; fruiting May–Dec. Dunes, plains, valleys, hillsides, arroyos, sandstone, sandy and gravel soils, caliche, prairies, mesquite savanna, oak woodland; 10–300 m; Tex.; Mexico (Coahuila, Nuevo León, Tamaulipas).

Matelea parviflora is uncommon to occasional in the South Texas plains. The species consists of several geographic variants differing in aspects of corolla and corona morphology. The most common form has green reticulate corollas with strongly reflexed lobes that are hirtellous adaxially only at the base and coronas composed of outer segments with elongate lateral lobes at the apex and very long, erect inner segments—together forming a trident. Less common variants have olive or purple corollas, corolla lobes that are spreading and/or densely hirtellous across the adaxial surface, minutely lobed outer corona segments, or short inner corona segments. This circumscription includes specimens that have been commonly identified as M. brevicoronata, although they differ conspicuously in one or more attri­butes of the type. For distinctions with the very similar M. brevicoronata, see discussion under that species. An illegitimate combination in Gonolobus was made by A. Gray at a time when the species was treated under a broad concept of that genus.