Chiefly perennial herbs, papillose on young growth. Leaves opposite and petiolate, entire, flat. Inflorescence an axillary dichasium; flowers bisexual, each subtended by a bract and a pair of membranous bracteoles; perianth segments 5, in a single whorl, shortly fused at base, margins membranous, each segment with a small dorsal spur just below the apex; stamens 5–12; ovary superior, 2-locular; styles 2; ovules 2 per locule. Fruit a circumsciss capsule, the 'lid' splitting equally into 2 parts; seeds 4, black, wrinkled.
3 species, 1 each in Africa, India and Australia, united by some authors into a single widespread species, Z. decandra.