Shrub or tree (0-3-)l-10(-12) m tall, bushy or slender, with branches ascending tospreading. Stems red to yellow-brown when young, soon 2-lined, eventually terete; internodes 2-6 mm long, much shorter than leaves; bark dark brown to grey. Leaves sessile; lamina ( 1 1- ) 15-45(- 60) x 2-5-12 mm, ± narrowly elliptic to narrowly oblongor very rarely oblanceolate, acute, margin plane to recurved, base cuneate, reflexed-auriculate, paler beneath, sometimes glaucous, subcoriaceous to chartaceous, lower ones ± soon deciduous; venation: (1)3-5 basal or near-basal veins, laterals branching dichotomously (mostly near the base), with numerous parallel or interrupted and ± vestigial secondary veins, without or with 1-8 cross-veins and a loose or ±dense tertiary reticulum; laminar glands in secondary venous system either (i) not interrupted and alternating with ± irregular series of small dots and short streaks or (ii) interrupted and wholly streaks and lines or with a few dots; marginal glands pale to dark, sparse to dense. Inflorescence 1-flowered; pedicel 1-8 mm long; bracts foliar but smaller and broader. Flowers (35)40-80 mm in diam., stellate; buds ovoid to subglobose, acute to rounded. Sepals 5-18 x 3-9 mm, imbricate, ± unequal, soon recurved in bud, broadly to narrowly ovate or subcircular, acute to subrounded, margin entire or usually ± irregularly glandular-denticulate or -ciliolate, midrib undifferentiated or obscure; laminar glands linear, numerous; submarginal glands absent or dark; marginal glands absent or dark. Petals orange-yellow to golden-yellow, flushed red to orange outside, persistent, spreading, 15-40(-43) x 5-26 mm, 2-3-3 x sepals, obovate-oblanceolate to oblanceolate, with apiculus small, rounded; margin entire or with a few dark sessile glands or glandular cilia; laminar glands linear, interrupted distally. Stamen fascicles persistent, each with 30-40 stamens, longest 11-20 mm long, c. 0.5 x petals, with filaments united for c. 1 mm. Ovary3.5-9 x 3.5-5.5 mm, ovoid to ovoid-globose; styles 4-12 mm long, 0.8-1.6 x ovary, c. 0.8 coherent, spreading distally; stigmas subglobose to narrowly capitate. Capsule 9-15 x 7-11 mm, ovoid to subglobose. Seeds reddish-brown, 1.2-1.5 mm long, ± narrowly cylindric, sometimes narrowly carinate and/or with distal expansion, finely linear-reticulate.
2n = 24 (both subspecies).
In open forest, forest margins, savannas, and grassland; 900-4000 m.
From SW. Arabia and Ethiopia to the Transvaal; also in Cameroun and Fernando Poo. Maps 1,2.
H. revolutum comprises two subspecies (Robson, 1979), one widespread (subsp. revolutum), the other confined to the East African mountains (subsp. keniense).