An herbaceous to suffruticose plant, the branchlets terete, pubescent or glabrate, sparingly-or densely armed with broad-based, black-tipped thorns. Leaves mod-erate or moderately large, sensitive, bipinnate, the pinnae 3-5 (usually 4) pairs clustered at the apex of the petiole (hence subdigitate), the leaflets usually about 30 or more pairs; petiole elongate, up to 8 cm. long, eglandular, usually setose; rachis very condensed, scarcely 3 mm. long; pinnae as much as 12 cm. long, the basal pinnular pulvinus setose; leaflets linear, 4-9 mm. long and usually 1-2 mm. wide, usually acute apically, inequilaterally rounded basally, the costa and remote lateral veins subprominent, glabrous except setose marginally and occasionally below; stipules linear-lanceolate, falcate, about 5 mm. long, setose. Inflorescence of axillary, pedunculate heads or very short spikes; peduncles short, usually little more than 1 cm. long; heads dense, many-flowered; floral bractlets sublinear, setose-laciniate. Flowers pinkish or purplish, sessile; calyx extremely minute; corolla funnelform, about 2 mm. long, glabrous, 4-lobed; stamens 4, several mm. long, free; ovary glabrous, bilateral, the style equalling the stamens. Legumes typically in a dense cluster, usually 10-15 mm. long and about 4 mm. wide, flat, glabrous, segmented, somewhat constricted between the articulated, 1-seeded segments, heavily setose-aculeate on the margins, the margins persisting after dispersal of the segments.
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