Sulphur Cassia is a large shrub or small tree. Young shoots are hairy, later hairless. Leaves are 15-30 cm, with a club-shaped gland 1-2 mm on rachis between each of lowest 2 pairs of leaflets. Stipules are caducous, linear. Leaf-stalks are 3.5-6.5 cm. Leaflet stalks are about 3 mm. Leaflets are 4-6 pairs, usually 5 pairs, abaxially farina-white, greenish above, ovate or elliptic, 3.5-10 × 2.5-4 cm, base broadly cuneate or subrounded, apex obtusely rounded or inconspicuously emarginate. Flower racemes occur in axils of leaves in upper part of branches. Peduncles are 3-10 cm; rachis 1-6 cm; bracts ovate, 3-8 mm, apex acute, finally reflexed. Flower-stalks are 1-3 cm. Sepals green to reddish brown, unequal, outer 2 suborbicular, about 3 mm in diameter, inner 3 obovate, 6-9 mm. Petals are bright yellow (drying orange or pinkish brown), ovate or obovate, 1.5-2.5 cm, 5-veined, clawed. Stamens are 10, all fertile, with short, thick filaments, lowest 2 with longer filaments; anthers subequal, opening by short, apical slits. Ovary hairy; style glabrous. Legume glossy, flat, straight, strap-shaped, dehiscent, 12-20 × 1.2-1.8 cm, with long, slender beak on top, valves papery. Seeds 20-30, oblong-elliptic, ca. 7 × 4 mm.