Enslenia ligulata Bentham, Pl. Hartw., 290. 1849; Cynanchum sinaloense (Brandegee) Woodson; Mellichampia sinaloensis (Brandegee) Kearney & Peebles

Latex white. Stems densely puber­ulent in single line; dwarf axil­lary branches rare. Leaves: 1 stipular colleter on each side of petiole; petiole 1–4 cm, densely puberulent in single line; blade pinnipalmately veined, ovate or deltate, 2.5–6.5 × 1.5–6 cm, chartaceous, base deeply cordate, with 2–8 laminar colleters, margins puberulent-ciliate or gla­brate, apex acute, attenuate, acuminate, or apiculate, surfaces minutely pilosulous on veins abaxially, glabrous adaxially. Inflorescences racemiform to corymbiform, soli­tary at nodes, 3–10-flowered; peduncle 1–5.5 cm, densely puberulent in single line; bracts caducous, 1, at base of each pedicel. Pedicels 5–15 mm, densely puber­ulent in single line. Flowers: calyx lobes spreading to reflexed, linear-lanceolate, acute to acuminate, 4–5 mm, ciliate; corolla cream, yellowing with age, deeply cam­panulate, tube 2–3 mm, lobes erect to spreading with recurved tips, linear-lanceolate, 7–8 mm, with thick­ened, proximally pilose, inframarginal ridges adaxially, gla­brous abaxially; corona united to column near base, composed of 5 segments connate at base, cream, lam­inar, exserted from corolla, subulate, apex incurved, unlobed, 6–11 mm; style apex convex. Follicles lance-ovoid, 6–9 × 1.5–3 cm, apex obtuse, thick-walled. Seeds 50–100, brown, 8.5–10 × 4–6 mm, narrowly winged, chalazal mar­gin erose, faces minutely papillate; coma white, 1.5–3 cm.

Flowering Jul–Aug; fruiting Sep–Oct. Streamsides in oak grasslands and mesquite grasslands; 1100–1600 m; Ariz.; Mexico.

Cynanchum ligulatum has the showiest flowers of the species of Cynanchum in the flora area. Flowering can be profuse on vigorous plants that blanket supporting vegetation. Such displays exude a strong, sweet perfume. Cynanchum ligulatum is in the flora area only in extreme southeastern Arizona (Cochise, Pima, and Santa Cruz counties), where it is rare along perennial or ephemeral streams. Several of the few known localities have been explored repeatedly by botanists; the scarcity of collections suggests that populations may be ephemeral, that plants do not regularly emerge or flower, or that the species is in decline at the edge of its range. Cynanchum ligulatum ranges south in western Mexico to Guanajuato and Michoacán. Southern populations have dark reddish or purplish corollas, although pale- or white-flowered plants are regularly encountered there as well. Those in Arizona and northern Mexico (Chihuahua, Sinaloa, and Sonora), have uniformly cream-colored corollas that are somewhat smaller than those from southern populations. The conservative approach by E. Sundell (1981) is fol­lowed for now. Should additional study support recog­nition of two species, C. sinaloense is available for north­ern populations, including the flora area.