Tree up to 15 m high or less frequently a shrub to 4 m high; trunk to 1 m in diam.; crown rounded, the branches often drooping somewhat, or flattened and spreading. Bark dark greyish-brown to blackish, rough, fissured, often flaking off in thick ± woody sections when old; young branchlets pale to dark grey- or reddish-brown to purple, sometimes as though whitewashed over a purplish background, often flaking minutely, glabrous or subglabrous, seldom pubescent. Stipules spinescent, in pairs, 0,5-5(10) cm long, usually rather stout, often thickened below and fused together basally into an enlarged "ant-gall", 1,5-2 x 2-2,5 cm, sometimes furrowed down the middle, taper­ing to a sharp point apically; other prickles absent. Leaves: petiole 0,4-1,4 cm long, adaxial gland absent; rhachis (0)1-3,5(5,5) cm long, glabrous or subglabrous, a small gland at the junction of each pinna pair; pinnae (1)2-5(6) pairs; rhachillae (1,3)1,6-3,2(4,2) cm long, glabrous or subglabrous; leaflets (6)8-15(18) pairs per pinna, 4-11,5 x (0,7)1,4-2,4(4) mm, linear-oblong to nar­rowly obovate, oblique basally, apex rounded to subacute, glabrous throughout or some­times marginal cilia present, rarely pubescent below, lateral nerves prominent and con­spicuous above and beneath. Inflorescences capitate, on axillary peduncles, solitary or fascicled, scattered along the shoots. Flowers bright golden-yellow, sessile or shortly pedi­cellate, (sometimes some flowers are male only); peduncles (1,8)2,3-4(5,5) cm long, glabrous or subglabrous, eglandular; involu-cel apical. Calyx glabrous, sometimes apices of lobes with few glandular hairs, tube 1,5-2,2 mm long, lobes up to 0,6 mm long. Corolla glabrous or apices of lobes with glandular hairs, 2,7-3,6 mm long, lobes sometimes free for most of their length. Stamen-filaments free or connate into groups basally, up to 7,5 mm long; anthers with a deciduous apical gland. Ovary 1,2-2 mm long, sessile or shortly stipitate, glabrous at first but soon becoming pubescent. Pods densely grey-velutinous all over, with nume­rous minute dark reddish-brown to purplish glands particularly when young, (4)6-13 cm long, 1,8-5 cm wide, 0,8-2 cm thick, indehiscent, semi-woody, frequently semi-lunate to suborbicular, sometimes curled almost into a circle, apex rounded to acute or beaked, spongy within, seeds irregularly scattered but separated by transverse partitions. Seeds dark reddish-brown, 8-14 x 7-10 mm, lenticular to elliptic, sometimes scarcely compressed; areole 3-9 x 2-5,5 mm. Tree to 7 m high; crown rounded, spreading, branches usually drooping some­what; habit resembling that of A. erioloba. Bark dark greyish-brown to blackish, rough; young branchlets grey or reddish-brown to purplish, sometimes appearing as though whitewashed over a purplish background, glabrous to densely grey-tomentellous, glan­dular or eglandular. Stipules spinescent, in pairs, 0,3-5 cm long, slender but usually stouter than in A. haematoxylon, never inflated as in A. erioloba. Leaves distinctly bipinnate, sparingly to densely grey-tomentel­lous: petiole 2-9 mm long, adaxial gland absent; rhachis 0,9-4,8 cm long, with or without minute scattered glands, a small yellowish-brown gland often present at the junction of each pinna pair; pinnae 3-12 pairs; rhachillae 0,4-2,2 cm long, glandular or eglandular; leaflets greyish, 11-25 pairs per pinna, 1-4 x 0,4-1,1 mm, linear to linear-oblong, often slightly falcate, apex rounded to subacute, sparingly to densely puberulous above and below, lateral nerves not prominent. Inflorescences capitate, on axillary peduncles, solitary or sometime