Cynanchum unifarium

Latex white. Stems puberulent in single line or glabrate; dwarf axillary branches rare. Leaves: 1 stipular colleter on each side of petiole; petiole 1–7 cm, densely puberulent in single line; blade pinnipalmately veined, ovate to deltate, 3–11 × 1.5–9 cm, chartaceous, base shallowly to deeply cordate or sagittate, with 2–6 laminar colleters, margins puberulent-ciliate, apex acute, attenuate, acuminate, or apiculate, surfaces sparsely puberulent on veins abaxially and adaxially. Inflorescences racemiform to corymbiform, solitary at nodes, 4–20-flowered; peduncle 0.6–3.5 cm, densely puberulent in single line; bracts caducous, 1, at base of each pedicel. Pedicels 4–12 mm, densely puberulent in single line. Flowers: calyx lobes ascending to spreading, lanceolate to oblong, 2–3 mm, apex acute, ciliate; corolla green with lobe margins and apex white, shallowly campanulate to campanulate-rotate, tube 0.5–1 mm, lobes ascending to spreading with recurved tips, oblong, 3–4 mm, glabrous, with thickened inframarginal ridges adaxially; corona united to column near base, composed of 5 segments connate at base, cream, laminar, included in corolla, quadrate, apex shallowly 3-lobed, central lobe equal to lateral lobes or extended as triangular tooth up to 8 times length of lateral lobes, 1–2 mm; style apex convex. Follicles ovoid, 8–12 × 1.5–2.5 cm, apex obtuse, thick-walled. Seeds 50–100, brown, 6–8 × 4–5 mm, narrowly winged, chalazal margins erose, faces minutely papillate; coma white to tawny, 2.5–3.5 cm.

Phenology: Flowering Apr–Oct; fruiting Jun–Jan.
Habitat: Limestone or igneous hills and valleys, alluvium, rocky slopes, canyons, streamsides, thickets, thornscrub, oak and juniper woodlands, grasslands, climbing trees, shrubs, and boulders.
Elevation: 0–1600 m.

Tex., e, n Mexico.

Discussion

Cynanchum unifarium occurs in a great diversity of habitats from southern to western Texas and is one of the most commonly encountered milkweed vines in the state. It is most commonly found in riparian vegetation but can occur in a wide variety of plant communities on diverse substrates. Cynanchum unifarium was included in a broadly circumscribed C. racemosum (Jacquin) Jacquin by E. Sundell (1981). This approach has merit, but the narrower concept used by W. D. Stevens (2009) is adopted here until this complex receives more detailed study. The Spanish common name derives from an Aztec word that is commonly applied to diverse milkweeds across Mexico, including those in the genera Asclepias, Gonolobus, Marsdenia R. Brown, Matelea, and Polystemma, among others.

Selected References

None.

Lower Taxa