Annual, sometimes aquatic, herbs. Stems 4-angled. Leaves opposite, decussate, the leaf venation pinnate. Flowers axillary, usually borne 2-6 together in fascicles or on minute branches, sometimes solitary. Bracts present, linear. Calyx 2-lipped and 5-lobed, prominently winged along the veins in fruit. Corolla 2-lipped and 4-lobed; tube cylindric below, slightly wider above; upper lip entire; lower lip larger with 3 subequal lobes. Stamens 4, fertile, didynamous. Nectary present, prominent, saucer-shaped. Ovary 2-locular, with hairs at the apex; locules with unicellular hairs inside; ovules many. Fruit a septicidal or poricidal capsule. Seeds numerous, small, with thickening of some epidermis cell walls. Worldwide: c. 40 species in the tropics, occurring mainly in Africa, SE Asia and the Indian Ocean islands. Zambia: 1 taxon. |
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