Tall annual herbs, stems villous. Leaves opposite, usually linear; stipules absent. Flowers terminal or in upper axils, in lax dichasia or solitary, 5-merious, bisexual; epicalyx absent; calyx tubular, 10-veined, 5-lobed, the lobes as long or longer than the tube; petals 5, entire, tapering into a distinct claw; stamens 10, 5 united to petals; ovary 1-celled with numerous ovules, styles 5. Capsule opening by 5 teeth; seeds numerous, reinform, tuberculate.
2 species, native to Eurasia; 1 species naturalised in Australia.