Perennial herbs. Stem simple to highly branched at inflorescence, 4-angled, angles smooth, narrowly winged. Leaves opposite. Inflorescences extremely congested, many-flowered cymes, clustered at leaf axils. Flowers 8-merous, regular, sessile. Calyx with short tube and 8 teeth; teeth linear or narrowly linear-lanceolate, acuminate. Corolla persistent in fruit; tube cylindrical; lobes spatulate to obovate, apex deeply notched, never truncate, with filiform awn arising from median of notch. Stamens overtopping stigma; filaments inserted on corolla tube; anthers free, oblong, apiculate. Ovary unilocular; style distinct. Capsule bivalved. Seeds numerous, surface distinctly winged.
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