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DescriptionAnnual or perennial herbs or small shrubs. Stems usually 4-angled. Leaves opposite, decussate, rarely in whorls of 3 or alternate, entire. Inflorescence of lax or dense axillary cymes, sometimes capitate and enveloped by large bracteoles or flowers solitary. Flowers bisexual, 4-8-merous, with bracteoles which are very variable in size. Calyx tube 8-16-ribbed; appendages 0 or present. Petals 0-8. Stamens 4-23. Ovary 2-5-locular. Capsule opening by an apical operculum, the lower part subsepticidal or dehiscing irregularly.