Chihuahuan hairy milkvine

Gonolobus chihuahuensis A. Gray, Proc. Amer. Acad. Arts 21: 398. 1886

Herbs. Stems 4–20+, prostrate, 10–50 cm, hispid to hirsute with long eglandular and minute glandular trichomes. Leaves with 1 or 2 colleters on each side of petiole; petiole 0.2–1.6 cm, hirsute with long eglandular and minute glan­dular trichomes; blade deltate (ovate), 0.7–3.3 × 0.7–2.6 cm, base shallowly to deeply cordate, with 2–4 laminar colleters, apex acute, surfaces densely hirsute with long eglandular and minute glandular trichomes. Inflorescences solitary, umbelliform, extra-axillary, pedunculate, 2–5-flowered; peduncle 0.1–0.3 cm, hirsute with long eglandular and minute glandular trichomes. Pedicels 3.5–5 mm, hirsute with long eglandular and minute glandular trichomes. Flowers: calyx lobes spreading, elliptic, 1.9–3.5 mm, apex acute, hirsute with long eglandular and minute glandular trichomes; corolla cream with green to pink striations that become reticulate at lobe margins, rotate-campanulate, tube 0.5–1.5 mm, lobes spreading to ascending, plane, oblong to spatulate, 2.4–5 mm, hirsute adaxially at base of lobes; corona united to column near base, composed of 5 united segments forming a short ring, segments arching over style apex, translucent white to pink, ligulate, 1.5–2 mm, densely, minutely hirtellous; apical anther appendages pink, deltoid; style apex pale to dark pink, rounded, convex. Follicles faintly striate, lance-ovoid (ellipsoid), 4.9–5.7 × 1.7–2.5 cm, apex acuminate, densely muricate, densely villous to hirsute with long eglandular and minute glandular trichomes. Seeds tan to brown, oval to ovate (orbicular), 7–9 × 5–7 mm, margins broadly winged, chalazal end erose, faces rugose; coma 1.5–3 cm.

Flowering Jun–Oct; fruiting Jul–Oct. Desert grass­land, hillsides, valleys; 1200–1500 m; N.Mex.; Mexico (Chihuahua).

Matelea chihuahuensis was reported in the United States apparently for the first time in 2013 by surveyors in the western piedmont of the Animas Mountains, in the bootheel of New Mexico (Quinn s.n., OKLA; A. McDonnell et al. 2015). However, an earlier collection was made in 1977 in the nearby San Simon Valley (Moir s.n., COLO). Because of its recent discovery in the United States, M. chihuahuensis has not been formally assessed for conservation status; with few known populations limited to Hidalgo County, New Mexico, this species should be considered to be of conservation concern. It is distributed across the state of Chihuahua, Mexico, but is apparently rare throughout its range. In New Mexico and in the bulk of its range in the foothills of the Sierra Madre Occidental in Chihuahua, it occurs in desert grassland in valleys and on mountain slopes. The white and green corollas, hirtellous corona segments, and small follicles are unusual in comparison to related species.

SELECTED REFERENCE McDonnell, A. et al. 2015. Matelea chihuahuensis (Apocynaceae): An addition to the flora of the United States and a synopsis of the species. J. Bot. Res. Inst. Texas 9: 187–194.