Description:Euphorbia ingens (Giant euphorbia) is a spiny, succulent medium-sized to large trees 4–12(15) m tall, with a sturdy main stem and a massive dark green crown branching in a broadly obconical manner or in the shape of an over-sized egg-cup and not distinctly candelabra-like. Euphorbia ingens is very similar to Euphorbia candelabrum from the Horn of Africa and eastern Africa, and may be conspecific. The branches of Euphorbia ingens are usually more distinctly and shortly segmented, the teeth along the angles are usually further apart and the branch tips bear fewer inflorescences.
Stem: Trunk stout simple; bark rough fissured grey. Branches robust, about 3 m upwards, erect or ascending, rebranching, high succulent, leafless, usually 4- or 5-angled, straight, subparallel, all attaining to about the same general level, with parallel sides. Lower branches not shed with age as in many other species. Flowering branches 4-angled, usually constricted at irregular intervals into oblong segments 7-15 (or more) cm long , 5-7.5 (12) in cm diameter, square in cross-section to distinctly but stoutly winged. Angles wing-like, 5-6 mm thick at the obscurely crenate or sinuate margin, 2-3 cm broad, bearing shallow tubercles 1–2 cm apart deep green.
Leaves: Rudimentary and scale-like, 2-3 mm long, obovate or broadly ovate, acute, with a hard rigid dark brown auricle (stipule) on each side at the base, glabrous, soon deciduous.
Spines: Spineless or with a pair of reduced spines 0.5-2 mm long borne on separate Spine-shields that do not form a continuous ridge. Spine-shields 12-18 mm apart, 4-5 mm in diameter, suborbicular or transversely elliptic or reniform, usually poorly developed and formed of a thin rust-colored disintegrating substance.
Inflorescences: Born in profusion along the margins at stem tips on flowering-eyes nearly or quite contiguous to the spine-shields. Each flowering-eye with 3 cymes on stout peduncles 2-3 mm long, bearing 3 cyathia, all at first sessile, the lateral ultimately on very short branches. Bracts 3-5 mm long, 4-6 mm broad, very broadly rounded, obtuse or subacute, concave, glabrous.
Flowers (cyathia): Very small greenish yellow to bright yellow 8-10 mm in diameter, cup-shaped or somewhat obconic, glabrous outside, with 5 glands and 5 transversely oblong or subquadrate fringed lobes. Glands contiguous, 3-5 mm in their greater diameter, somewhat half circular in outline when seen from above, and from beneath somewhat triangular with rounded auricles at the base, thick and fleshy, with a sharp ridge along their inner margin, thence sloping to the acute edge of the outer margin, smooth, light green. Perianth irregularly divided into 3 or more filiform lobes 2–4 mm long, sometimes with 1 or 2 teeth.
*Female flower: Styles 3 (rarely 2), 3–3.5 mm long, joined for 1.5 mm, apices thickened, rugulose, bifid. Ovary at first subsessile, with a conspicuous 3-lobed calyx at its base, becoming exerted in young fruit on a stout pedicel as long as the cyathium, glabrous.
Male flowers: Many, bracteoles spathulate, plumose; stamens c. 5.5 mm long.
Fruit (capsules): Shortly exerted on a stout pedicel 5 mm long, (2)3-locular, almost globose, erect, 7-10 mm in diameter, green becoming reddish, with the outer substance evidently somewhat fleshy, glabrous, hardening immediately before dehiscence to 6 × 9 mm, and very obtusely (2)3-lobed.
Seeds: 3-4 mm long, subglobose to ellipsoid, slightly compressed laterally,, with a slight groove down the ventral side, and a slight keel down the dorsal, very faintly and minutely tuberculate as seen under a lens, greyish-brown speckled with paler brown, smooth.