Arizona milkvine

Lachnostoma arizonicum A. Gray, Proc. Amer. Acad. Arts 20: 296. 1885; Matelea arizonica (A. Gray) Shinners

Stems densely pubescent, pubes­cence of internodes ubiqui­tous, trichomes eglandular only. Leaves: petiole 1.2–2.7 cm, pubescent; blade deltate, 1.9–4.5 × 0.9–2.5 cm, base cordate, apex acute to acu­mi­nate, surfaces pubescent, hairs eglandular, colleters 4–5, 0.3–0.5 mm. Peduncles to 32 mm, pubescent. Pedicels 0.8–1.3 cm, pubescent. Flowers: calyx lobes lanceolate, 3.7–5.3 × 0.8–1.4 mm, margins entire, apex acute to obtuse, abaxial surface pubescent, adaxial surface glabrous; corolla white or light yellow, green reticulate-veined, campanulate at base, tube 2.9–5 × 2.9–3.7 mm, lobes oblong to ovate, 3.8–5 × 2.8–3.7 mm, slightly lobed at base, glandular swelling frequently present in sinus, apex obtuse, abaxial surface pubescent, adaxial surface pubescent toward base; corolline corona absent; gynostegial corona connate approximately 1/2–3/4 dis­tance from base and adnate to corolla; style-head ca. 3 mm diam., stipe 1.6–1.9 mm; dorsal anther appendages 0.2 × 0.9 mm, apex emarginate; pollinia suborbiculate to rhombic, 0.2 × 0.15 mm. Follicles narrowly ovoid, 7.5–8.4(–11) × 2.3–3.7 cm, surface minutely pubescent (appearing glabrous). Seeds 5.9–6.4 × 3.9–4 mm, distal margin entire, surfaces glabrous, coma white, to 1.5 cm.

Flowering Jul–Nov; fruiting Jun–Feb. Canyons, streambeds, cliff bases; 900–1400 m; Ariz.; Mexico (Baja California Sur, Sonora).

In the United States, Gonolobus arizonicus is restricted to south-central Arizona (Graham, Pima, and Santa Cruz counties).