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DescriptionAnnual or perennial herbs with entire, opposite leaves. Inflorescence terminal on the stems and branches. Bracts persistent. Fertile flowers in a group of 3, the outer pair with bracteoles and subtended laterally by 2 modified sterile flowers consisting of a number of strongly hooked spines. Bracteoles sometimes with a hooked awn. Perianth segments 5. Stamens 5, alternating with pseudostaminodes. Fruit a thin-walled capsule.