Description from Flora of China
Herbs, annual, biennial, or perennial, rarely woody at base. Stems erect, with a tough cortex, glabrous or rarely pubescent. Stipules small or absent. Leaves alternate or opposite, simple, sessile, with 1 or 3(or 5) veins from base, margin entire or sometimes denticulate and sometimes apically with glandular trichomes. Inflorescences cymes or scorpioid cymes. Flowers bisexual, regular, sometimes heterostylous. Sepals 5, imbricate, persistent, margin entire and sometimes with glandular trichomes. Petals 5, red, white, blue, or yellow, fugacious, longer than sepals, contorted, base clawed. Stamens 5, alternate with sepals; filament bases connate; staminodes 5, dentiform. Ovary 5-loculed or appearing 10-loculed by intrusion of false septa, with 2 ovules per locule; styles 5, filiform; stigmas capitate. Capsule splitting into 10 segments. Seeds compressed, shiny, with mucilaginous testa.
The greatest species diversity is in the Mediterranean region.
About 180 species: temperate and subtropic regions; nine species (one introduced) in China.