Shrubs or trees; plants monoecious (Africa) or dioecious (Madagascar); bark longitudinally striate, sometimes lenticellate. Leaves alternate or opposite, often discolorous, caducous or persistent on mature stems, estipulate; leaf blades glabrous adaxially, sparsely covered with inconspicuous adpressed indument abaxially or glabrescent (trichomes c. 0.5-1 mm long), margin entire, ± revolute; midrib grooved adaxially, raised abaxially; venation brochidodromous; fine venation reticulate; leaf buds conduplicately folded, covered with dense indument; petioles grooved adaxially, articulate, drying darker than midrib. Inflorescences axillary and fasciculate (Malagasy species), or lateral (or sublateral) and borne on short woody compact racemose axes (African species); inflorescence bracts absent; pedicels articulate. Flowers white, small, bisexual or unisexual; staminate and pistillate flowers of similar size and shape; floral tube absent; sepals 4-6, imbricate, reflexed or spreading, rarely erect, persistent in fruit; petals scale-like, 4 or 5 (10), bifid, divided nearly to base, adnate to receptacle, persistent in fruit; stamens twice the number of petals, (8) 10 (12) (20), straight in bud, ± inserted in a single whorl, persistent in fruit; anthers oblong, introrse, basifixed. Staminate flowers with a minute pistillode; pistillode obscured by many erect receptacle trichomes. Pistillate flowers with (8) 10 (12) (20) persistent staminodes; rudimentary anthers globose or undifferentiated; subgynoecial disc absent; gynoecium 3-6-carpellate, sessile; carpels uniovulate; ovary superior, usually one to several locules aborting, densely pubescent, surrounded by many erect receptacle trichomes; ovules minute, anatropous, pendulous; style terminal, straight, persistent; stigma globose, lobed, papilliate. Fruits green-yellow or white (O. casearia), loculicidal capsules, subspheroidal to ovoid-pyramidal, developed carpels producing longitudinal lines of dehiscence; dehiscence lines depressed or ± plane, often bicarinate on both sides of line; pericarp dry and thin, or fleshy and thicker. Seeds brown or black, ovoid, triangular or circular in cross section, edges rounded, adaxial side often costate, curved, abaxial side costate, other sides curved or ± flat; seed coat crustaceous, thin, outer epidermis puberulent, indument red-orange, denser near poles, inner epidermis finely striate; endosperm copious; cotyledons longitudinally curved, thin (c. 0.5-1.5 mm thick).