Euphorbia clavarioides is one of many low-growing succulent plants. It forms a small, cushion-like mound, low on the ground, up to 50–70 mm high and 100–300 mm wide. The clump is composed of masses of cylindric, spineless, leafless, succulent stems, the tips forming the rounded edge of the cushion. The rootstock is a continuation of the main stem, which is fleshy, thick and buried underground, and covered all the way to the middle of the flattened body, by crowded branches. The main branches are cylindric and covered in tubercles. The leaves are small, fleshy, deciduous, 10–20 mm long and 5–10 mm wide, channelled all the way down the face, with a hairless surface. They are borne at the tips of the stems and soon fall off.

The inflorescences, known as cyathia, appear to be single flowers, but each is a cluster of very reduced flowers, inside a cup-like structure with petal-like bracts. The tiny flowers are unisexual and are reduced to a single stamen or a single ovary. The cyathia are solitary, stemless, yellow, have 3 to 5 bracts and are borne at the tips of the stems in spring and early summer (from September to February).

The fruit is a capsule, about 8 mm in diameter, attached directly by its base, without a stalk or peduncle, producing dark brown seeds that are 3.5 mm in diameter.