Vines perennial, with short tuberous roots. Stems often reddish pigmented, prostrate or twining, to 300 cm, slender, terete or angulate, usually sparsely to densely covered with spreading, straight hairs, often yellowish, interspersed with white, hooked hairs. Leaves: stipules ascending or spreading, triangular to widely ovate or orbiculate, 4–7 × 3–4 mm, acute or obtuse, sometimes auriculiform, 3–many-veined, glabrate or strigillose, ciliate; petiole 1–5(–8) cm; rachis 0.5–2 cm; stipels usually triangular to lanceolate, 1–3 × 1 mm, acute; leaflet blades narrowly to widely ovate, often with a basal lobe, 1.5–9 × 1–7 cm, membranous or thin, rarely leathery, base broadly cuneate, apex obtuse or acute to long-acuminate, sur­faces usually sparsely strigose or hirtellous, often gla­brate. Peduncles to 30 cm. Inflorescences 20–56 cm, axis usually covered with uncinate hairs, if straight hairs present, then mainly on peduncle; rachis 5–12 cm, with 4–40 usually biflorous nodes, often scattered along rachis; primary bracts usually lanceolate, 2.5–7(–10) × 3–4 mm, 3–many-veined, ciliate, nectariferous. Pedicels arcuate or reflexed and thicker in fruit, 1–3.5(–5) mm, usually shorter than calyx, hairs straight and hooked; bracteoles persistent, ovate to subulate, 0.5–1.5 mm, usually 1-veined, ciliate, sometimes along pedicels. Flowers: calyx campanulate, 1.5–3.5(–4.5) mm, inner surfaces of tube strigillose, outer surfaces usually hirtellous, especially on lower lobe; abaxial and lateral lobes triangular, 0.5–1.2 mm, apex acute; adaxial lobes connate, apex emarginate; corolla pink, lilac, purple, or white, 10 mm; banner obovate to orbiculate, 4–8 mm, apex emarginate, glabrous; wings obovate, auriculiform, 0.5–1.4(–1.8) mm; keel 5 mm; ovary oblong, 2.5–5 mm, covered with hooked hairs or strigillose. Legumes pendent, compressed, usually linear-falcate, 10–33 × 3–7 mm, elastically dehiscent, valves thin, sparsely covered with long, incumbent and hooked hairs or glabrate, sessile. Seeds 2–6, brown or gray mottled with black, oblong, orbicular, or reniform, 2–4.5 × 1.9–4.3 mm, smooth; hilum ovate, 0.3 mm. 2n = 20.

Phenology: Flowering Apr–Jan.
Habitat: Clearings, margins and under­story of pine, pine-oak or oak forests, sandy slopes, rocky clay soils.
Elevation: 400–2300 m.

Distribution

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Ariz., Mexico, Central America (Costa Rica, El Salvador, Guatemala, Honduras).

Discussion

Phaseolus leptostachyus is distinctive with its short inflorescences and numerous flowers, primary bracts that are similar in shape to the stipules, and pedicels that are shorter than calyx and strongly curved soon after anthesis. Only three collections are known from the flora area, collected in the 1930s from Cochise and Maricopa counties.

Selected References

None.

Lower Taxa

None.