Darkstar milkvine

Vines, herbaceous. Stems 1–5, twining, often branched near base, 30–200 cm, short-hirsute with spreading to retrorse eglan­dular and minute glandular tri­chomes. Leaves with 1 colleter on each side of petiole; petiole 0.7–1.7 cm, short-hirsute with eglandular and minute glandular trichomes; blade ovate to lanceolate, 2.5–5 × 1–3.5 cm, base deeply cordate, with 2–4 laminar colleters, apex attenuate to long-acuminate, surfaces short-hirsute with eglandular and minute glandular trichomes. Inflores­cences solitary, umbelliform to somewhat racemiform, extra-axillary, pedunculate, 1–5-flowered; peduncle 0–1 cm, short-hirsute with eglandular and minute glandular trichomes. Pedicels 3–10 mm, short-hirsute with eglan­dular and minute glandular trichomes. Flowers: calyx lobes spreading, lanceolate, 2–3 mm, apex acute, short-hirsute with eglandular and minute glandular trichomes; corolla pale to dark maroon or green with maroon tinge, sometimes faintly striate and reticulate towards margins, rotate, tube 1–1.5 mm, lobes spreading, narrowly lan­ceolate, 5–7 mm, hirtellous abaxially, hirtellous adax­ially in ring at base of lobes, vestiture continuing along center of lobes with trichomes diminishing in height (reported to be rarely glabrous); corona united to corolla and column near base, composed of 5 united segments with outward flared margins, each with an adaxial incurved appendage, crimson to dark maroon, 0.5–1 mm, margins and appendages papillose; apical anther appendages white, brown at base, deltoid; style apex concave. Follicles gray-striate, ellipsoid to lance-ovoid, 8–11 × 1.5–2 cm, apex acuminate, smooth or with very sparse, low tubercules, glabrous. Seeds tan, ovate, 8 × 5–6 mm, margins thickly winged, chalazal end minutely erose, faces smooth; coma 4–5 cm.

Flowering May–Aug; fruiting Jun–Oct. Narrow can­yons, slopes, arroyos, limestone, rhyolite, rocky soils, riparian woodlands; of conservation concern; 1200–1600 m; Tex.; Mexico (Coahuila).

Matelea atrostellata is endemic to Chihuahuan Desert mountain ranges from the Chinati Mountains to the Sierra del Carmen. Within the flora area, it is uncommon and restricted to Brewster County, Texas, and likely threatened. It is evidently a close relative of M. producta and M. texensis based on similarity in vege­tative and fruit characters. However, the flowers diverge dramatically by their rotate corollas with outward-flared, papillose corona segments that are free from the corolla. Like M. texensis, M. atrostellata is found at the southeastern margin of the range of M. producta, and M. atrostellata does not co-occur with either species.