Fringed twinevine

Sarcostemma cynanchoides Decaisne in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 8: 540. 1844

Stems sparsely pilosulose, puber­ulent with curved trichomes, or glabrate, pilosulose to glabrate at nodes. Leaves persistent, stipular colleter 1 on each side of petiole; petiole 0.4–2 cm, puberulent with curved trichomes in a single line; blade ovate to lance­olate, 1.2–8 × 0.7–4.5 cm, chartaceous, base cordate, sagittate, or hastate, margins plane, apex acuminate to acute, venation pinnipalmate, surfaces sparsely pilosu­lose, mainly on veins, or glabrous, margins inconspicu­ously ciliate with ascending hairs, laminar colleters 4–6. Inflorescences solitary (paired) at nodes, 6–31-flowered; peduncle 1–6 cm, elongating in fruit, puberulent with curved trichomes; bracts caducous, 1, at base of each pedicel. Pedicels 8–20 mm, puberulent with curved tri­chomes. Flowers: calyx lobes lanceolate to ovate, 2–3 mm, apex acute, erect, pilosulose, ciliate, colleters 1 or 2, in sinuses, or absent; corolla cream, often rose-tinged at lobe tips or throughout, rotate, tube 1.5–2 mm, lobes spreading with ascending tips, ovate, 3–6 mm, apex acute to obtuse, sparsely puberulent with curved trichomes to glabrate abaxially, minutely hispidulous adaxially throughout or distally or glabrate, margins ciliate; corona ring green, cream, or pinkish, inflated corona segments proximally green, distally glossy white, ovoid, 1.5–2.5 mm; style apex shallowly convex. Fol­licles usually solitary, ovoid to lance-ovoid, 6–9 × 0.8–1.6 cm, apex long-acuminate, puberulent with curved trichomes. Seeds 20–50, brown, winged, biconvex, lanceolate, 5–6 × 2–3 mm, faces papillate, chalazal mar­gin erose; coma white, 2.5–3 cm. 2n = 20.

Flowering (Mar–)Apr–Oct; fruiting (Jun–)Aug–Nov. Canyons, cliffs, stream banks and terraces, flood plains, old fields, roadsides, sandy, silty, clayey, gravelly, or calcareous soils, sandstone, limestone, riparian, oak, and mesquite woods, grasslands, thorn scrub, desert scrub; 0–1900 m; Ariz., Ark., N.Mex., Okla., Tex.; Mexico (Chihuahua, Coahuila, Nuevo Léon, Sonora, Tamaulipas).

Funastrum cynanchoides is most similar to F. heterophyllum, and in the past these species were treated as conspecific (with the latter entity most com­monly recognized as Sarcostemma cynanchoides subsp. hartwegii). These species are most reliably distinguished by leaf shape (ovate to lanceolate with a cordate base in F. cynanchoides versus linear to linear-lanceolate with a hastate to truncate base in F. heterophyllum), corolla color (little to no pink in F. cynanchoides versus faintly to strongly pink to purple in F. heterophyllum), flower­ing phenology (summer in F. cynanchoides versus winter to spring in F. heterophyllum, although summer flower­ing is occasional), and habitat (grasslands in F. cynanchoides versus desert scrub in F. heterophyllum); however, as emphasized in earlier treatments, the distinguishing characteristics are not constant within species, and this is especially true in the contact zone from south­eastern Arizona to trans-Pecos Texas, where intermediates rep­resenting putative hybrids sporadically occur. These are most commonly encountered in Big Bend National Park. The effective isolation of these species is appar­ent in Tucson, Arizona, where F. heterophyllum occurs commonly in arroyos throughout the city and F. cynanchoides is adventive and common on fences; no intermediate specimens are known from this area. Funastrum cynanchoides is uncommon in Arkansas, and its conservation status should be evaluated in that state.