Seedlings to 1 m too, with an unbranched, 4-5 angled stem, heavily mottled with darker green; spine shields forming a continuous horny margin along the angles; spines paired, 3-7 mm long. Young plants to 3 m tall, branched; branches first ascending then drooping, obtusely 3-4 angled, uniformly grayish green, angles shallowly toothed, with robust, widely separated spine shields up to 1 cm long but progressively shorter as more branches are produced; spines to 12 mm long. Mature plants 3-6 m tall; primary branches spreading horizontally, secondary branches crowded towards the tips, densely rebranching; terminal branchlets cylindrical, spineless but with callose leaf scars 1-3 cm apart immediately below the flowering scars. Cymes solitary, 1-forked; peduncles and cyme branches 5-7 mm long. Cyathia about 9 mm in diameter; glands 4 mm wide, just touching, yellow; pistillate flowers with 3-lobed perianth about 1.5 mm long; styles about 3 mm long, with bifid, scarely thicked tips. Capsules exserted on erect pedicels about 1 cm long, deeply and acutely 3-lobed wtih truncate bases and tops, to 8 mm long and 20 mm wide, dark purplish grey; seeds subglobose, about 4 mm in diameter, smooth, pale greyish buff.
Euphorbia robecchii grows on red sand overlying limestone, often forming groves in wadis, at 50-825 m. It was reported from regions N1-3, C2, S1-3 in the Flora of Somalia. Its range extends to Ethiopia, Kenya, and northeastern Tanzania.