Perennial herbs or shrubs, rarely small trees (B. muelleri), glabrous or with simple and/or stellate hairs, unarmed. Leaves opposite (rarely alternate), simple or compound. Flowers solitary or in cymes or rarely cymose panicles, 4-merous or rarely 5-merous (B. scabra), bibracteolate. Sepals free. Petals free. Stamens 4 + 4, rarely 4 caducous (B. parviflora), inserted beneath disc, all or only 4 fertile; filaments inwardly curved, flat or semiterete, glabrous or hairy, often enlarged at apex and often with a subapical inflexed tip; anthers introrse, minutely or prominently white-apiculate or not. Disc prominent. Carpels 4; ovaries free, united at apex on adaxial margin by the solitary style.
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