The straight, paired thorns of Catophractes alexandri grow at the nodes immediately above the leaves, becoming about 5 cm long. The thorns are initially pale grey and densely woolly. They lose the hairs and become dark brown or almost black.
In picture the thorns are partly small side-branches, ending in spines. These thorns are very hard and sharp. One of the Afrikaans common names, papwieldoring (flat tyre thorn), tells that story (Mannheimer and Curtis, (Eds.), 2009; Coates Palgrave, 2002; Leistner, (Ed.), 2000; Van Wyk and Van Wyk, 1997; iNaturalist; Wikipedia).