Annual or perennial herbs (dwarf undershrubs in some non-Australian species); glabrous and glaucous, or glandular-hairy. Leaves opposite or pseudo-verticillate; bracts scarious, at least at the connate base. Flowers in heads or dichasia, rarely solitary, 5-merous, bisexual; epicalyx absent; calyx campanulate, 5-veined, green with scarious seams between veins, 5-lobed; petals exceeding calyx; coronal scales absent; stamens 10; ovary 1-celled, with several ovules, styles 2. Capsule narrow-obovoid, opening by 4 teeth; carpophore absent; seeds several, asymmetric-pyriform to subreniform, flattened, tuberculate, rarely smooth.
About 125 species, native to temperate Eurasia, especially the eastern Mediterranean; 2 species naturalised in Australia.