Vines perennial, with thick, elongate, tuberous taproots. Stems usually climbing, to 200 cm. Leaves: stipules ascending, spreading, or reflexed, oblong to triangular or lanceolate, 3–5.5 × 1–2.5(–3) mm; petiole 1–6.5(–7.3) cm; rachis 0.5–2 cm; stipels oblong-subulate, 1–1.5 mm, 1 or 2-veined; leaflet blades ovate to lanceolate, deeply 3-lobed, dissected, basal lobe rounded to quadrate, middle lobe triangular to oblong or linear-lanceolate, laterals (0.7–)2–5.5(–6.5) × (0.4–)1.3–4(–5.5) cm, terminal (1.5–)2.5–6.5(–7.5) × (0.5–)1.5–4.6(–7.5) cm, membranous to firm, base rounded to truncate, apex acute, surfaces glabrous or sparsely covered with ascending hairs, mainly along veins. Peduncles 1.5–18.5 cm. Inflorescences often also with lateral, floral branches, 5–30(–40) cm; main axis usually sparsely to densely covered with ascending (often retrorse) and uncinate hairs or glabrous; rachis usually 2.5–10 cm, with 3–14 often biflorous nodes; primary bracts ovate to lanceolate or broadly ovate, 1–5(–7) × 0.5–3.5 mm, 3–9-veined. Pedicels 3–10 mm, covered with only uncinate hairs or with ascending and interspersed uncinate hairs; bracteoles usually persistent, ovate to linear-lanceolate, 0.5–2 mm. Flowers: calyx campanulate, 2–3(–4) mm, glabrous or hirtellous to strigillose, abundantly so on abaxial lobe; abaxial and lateral lobes triangular; adaxial lobes connate; corolla usually pink or purple, rarely white, 12–15 mm; banner oblong to orbiculate, 10 mm, apex emarginate, glabrous; wings obovate, 12–16 mm; keel 5.5–9 mm; ovary linear, 4–6.5 mm, sparsely covered with appressed hairs. Legumes pendent, compressed, linear-falcate, 30–45(–51) × 8–10(–15) mm, elastically dehiscent, valves thin, sparsely covered with ascending hairs, sessile. Seeds 2–5(or 6), brown or gray, mottled with black, oblong to reniform, 4.2–7.5 × 3.5–7 mm, smooth; hilum oblong-ovate, 0.8–1.2 mm.

Phenology: Flowering Jun–Oct.
Habitat: Open pine or pine-oak forests, chaparral, rocky limestone or igneous soils.
Elevation: 1600–2800 m.

Distribution

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Ariz., N.Mex., Tex., Mexico (Aguascalientes, Chihuahua, Coahuila, Durango, Hidalgo, Jalisco, Nuevo León, Sinaloa, San Luis Potosí, Sonora, Tamaulipas, Zacatecas).

Discussion

Phaseolus scabrellus, which is mainly restricted to the Chihuahua Desert Region and adjacent mountains, is characterized by its deeply 3-lobed leaflets, basal lobes rounded to quadrate, and relatively small flowers. It is readily confused with P. filiformis, but the latter has fibrous roots, smaller flowers and fruits, and rugose seeds.

Selected References

None.

Lower Taxa

None.