Tree or shrub, 3–9 m high; bark yellowish green or whitish, turning brownish and powdery with age; young branchlets glabrous or nearly so, brownish, older ones with minutely flaking or powdery yellowish to brown bark. Stipular spines mostly straight, up to 7.5 cm long, some basally inflated and fused into ± deeply bilobed “ant-galls”. Leaves glabrous or nearly so; pinnae 1–4(–6) pairs; leaflets 3–10 pairs, 2–13(–20) x 0.5–6(–10) mm. Flowers bright yellow in heads which are typically arranged along short lateral branches; peduncles up to 2.5 cm long with the involucel at or near the base. Calyx 0.8–1.5 mm long. Corolla 2.25–2.5(–4) mm long. Pods linear, falcate to almost straight, 5.5–12 x 0.4–0.7 cm, finely longitudinally veined, blackish brown, glabrous. Seeds compressed, 6–7 x 3–4 mm.
