Euphorbia halemanui is a scandent (climbing) shrub in the Euphorbiaceae (spurge) family with stems 1 to 4 m (3 to 13 ft) long. The egg-shaped to inversely lance-shaped leaves are decussate (successive pairs of leaves at right angles to the previous pair). The leaves are 4 to 13 cm (1.6 to 5 in) long and 1 to 4.5 cm (0.4 to 1.8 in) wide, with persistent stipules (small appendages at the base of the leaf stems). Groups of flowers (cyathia) are in dense, compact, nearly spherical clusters or occasionally solitary in leaf axils. The stems of cyathia are about 2 mm (0.08 in) long, or if solitary, about 5 mm (0.2 in) long. The fruits are green capsules, about 3 mm (0.1 in) long, on recurved stalks, enclosing gray to brown seeds.