The stems of Euphorbia atrispina are described as having rounded angles, scalloped instead of triangular, when regarded in cross-section. Stem colour is a dull, dark green, the surfaces covered in a powdery coating. This plant is closely related to E. heptagona that has angular stem ridges, triangular in cross-section.

E. atrispina var. atrispina is one of two swartdoringnoorse of the Oudtshoorn to Ladismith region where they are endemic. The spines are black in this form, as the common name suggests. In the other subspecies, E. atrispina var. viridis the cyathia stems are greenish, the cyathia having more pointed bracteoles (JSTOR; iSpot; Smith, et al, 1997).