Herbs, perennial, to 2 m; branches green. Leaves meso­phyllous, 5.5–18 cm, very finely hairy to glabrate; stipules cadu­cous; extrafloral nectary 1, base of petiole, sessile, globose egg-shaped; leaflet pairs 4–8, blades ovate- or lanceolate-acuminate, 30–80 × 8–32 mm. Racemes usually 4–10-flowered; bracts caducous, green, equal to or shorter than bud. Pedicels 9–25 mm. Flowers mono­symmetric; calyx greenish or yellowish; corolla yellow, longest petal 10–15 mm; androecium heterantherous, stamens 7, staminodes 3; anthers of middle stamens 3.8–5.4 mm, of abaxial stamens 5–7 mm, elongated beyond pores, dehiscing by 2 pores, apical appendage short, linguiform, thickened; gynoecium incurved, ovules 60–78; ovary hairy; style incurved. Legumes ascending, flat, curved, 120–230 × 2.5–4.5 mm, shallowly corrugated over seeds, indehiscent. Seeds brown to brownish olive green, obovoid.

Phenology: Flowering mid summer–mid fall.
Habitat: Washes, riverbeds, thickets, secondary woodlands, grasslands, disturbed pastures, roadsides.
Elevation: 700–2100 m.

Distribution

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Ariz., N.Mex., Mexico (Aguascalientes, Chihuahua, Guanajuato, Jalisco, Michoacán, Morelos, Oaxaca, Sonora, Tamaulipas, Zacatecas).

Discussion

Varieties glaberrima and leptocarpa (Bentham) H. S. Irwin & Barneby are the only two varieties in which the adaxial surfaces of leaflets are glabrous or glabrate (H. S. Irwin and R. C. Barneby 1982). However, these two varieties have disjunct distributions, with var. leptocarpa occurring locally in northeast Argentina and adjoining regions of Brazil (Irwin and Barneby) and Paraguay (B. Marazzi et al. 2006b).

Selected References

None.

Lower Taxa

None.