This photo of Euphorbia cooperi taken in January in the Kruger National Park shows triads of buds along the spiny stem tip ridges. The central bud is positioned a little below the lateral ones and slightly further away from the tip.
The thin, sharp spines grow in angled-out pairs spaced on stem wings on continuous, horny spine ridges. The young spines are dark brown or purplish brown, old ones dry and grey. The spines are about 5 mm to 7 mm long, occasionally as long as 15 mm.
Below the branches on old, tree-like specimens of E. cooperi the lower stems parts will be bare and visible, because the lowest branches die and fall over time. Vertical rows of round holes are found in the pale grey bark on the stems where these lost branches had been attached, typical of the species (Smith, et al, 2017; Coates Palgrave, 2002; Schmidt, et al, 2002; Pooley, 1993; iNaturalist).