Conspicuously flat-crowned tree 6-15(20) m. high; bark rough and fissured, brown to nearly black; epidermis not peeling on the twigs; bark on young trees papery; indumentum of branchlets variable, pubescent to shortly villous, grey or somewhat yellowish. Stipules spinescent, other prickles absent; spines variable, absent, short or up to 7.2 cm. long, straight, ashen when elongate, never inflated. Leaves: petiole 2-5 mm. long; pinnae of well-developed leaves of mature shoots 15-51 pairs (reduced leaves with fewer pairs also present); leaflets up to 4 x 0.75 mm. Flowers in heads; stamens white; calyx and corolla red (? always). Corolla glabrous or inconspicuously puberulous on the lobes outside. Pods 5-13 x 1.2-2.1 (2.8) cm., subcoriaceous, straight or slightly curved, grey or brown, longitudinally veined, ± glandular and sometimes puberulous, narrowed at the base and sometimes at the top. Seeds ± oblique in the pod, olive-brown, 7-10 x 4-6 mm., smooth, elliptic, compressed, areole 6-7 x 2.5-4 mm.