Texas milkvine

Gonolobus productus Torrey in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 165. 1859

Vines, herbaceous (rarely suf­frutescent without corky bark). Stems 1–5, twining (at least at stem tips), 30–200 cm, short-hirsute with spreading to retrorse eglandular and minute glandular trichomes. Leaves with 1 or 2 colleters on each side of petiole; petiole 0.5–3 cm, short-hirsute with eglandular and minute glandular trichomes; blade ovate to lanceolate, 2.5–8 × 1–5.5 cm, base deeply cordate, with 2–4 laminar colleters, apex long-acuminate, sur­faces densely hirsute, eglandular. Inflorescences solitary (rarely paired), simple umbelliform or somewhat racemiform, extra-axillary, pedunculate, 2–8-flowered; peduncle 0.6–1.7 cm, short-hirsute with eglandular and minute glandular trichomes. Pedicels 4–9 mm, short-hirsute with eglandular and minute glandular trichomes. Flowers: calyx lobes ascending, elliptic to lanceolate, 2–4 mm, apex acute, short-hirsute with eglandular and minute glandular trichomes; corolla green to reddish abaxially, green to yellowish green with dark green reticulations (rarely brown) adaxially and a thin red to purple ring at top of throat, tubular-campanulate, tube 3.5–8 mm, lobes spreading, 5–7 mm, hirtellous abaxially, glabrous adaxially; corona concealed in throat, a ring with 5 lobes incumbent on backs of anthers, green to pinkish or lavender, 1–1.5 mm, glabrous; apical anther appendages greenish or yellowish cream, deltoid; style apex green to yellowish green, pentagonal, flat. Follicles gray-striate, fusiform to ellipsoid, 7–10 × 1.5–2.5 cm, apex acuminate, smooth, glabrous. Seeds tan, ovate, 6–8 × 4–5 mm, margins thickly winged, chalazal end minutely erose, faces smooth; coma 2–3 cm.

Flowering Apr–Sep; fruiting Jul–Oct. Hill slopes, bajadas, canyons, arroyos, gneiss, granite, limestone, sandstone, rocky, sandy, and clay soils, desertscrub, thornscrub, mesquite and juniper grasslands, chaparral, riparian and pinyon-juniper woodlands; 700–2000 m; Ariz., N.Mex., Tex.; n Mexico.

Matelea producta occurs in the flora area along a narrow arc from the Grand Canyon near Lake Mead in Arizona to the Trans-Pecos region of Texas and at scattered locations in northern New Mexico. Its tubular-campanulate green corolla is unlike that of any other milkweed vine in its range, except the very similar M. texensis, which differs by densely hirtellous corollas. However, M. texensis is narrowly endemic to a small region south of Alpine, Texas, just beyond the range of M. producta. The species are as of yet not known to co-occur. Many Matelea species have corollas that range in color from green to shades of maroon or brown. The corollas of M. producta are almost invariably green adaxially; however, a specimen gathered from the Davis Mountains of western Texas (Rintz 2006-1, SRSC) represents the only known occurrence of brown flowers in this species. Although milkweed vines in several genera are well known for ill-scented herbage, M. producta is particularly malodorous.