Description from Flora of China
Herbs annual, rarely perennial, much branched at base. Stems ascending, often decumbent. Leaves opposite, usually apparently verticillate with leaf-fascicles (short, leafy, lateral branches) on both sides of nodes, sessile; leaf blade linear, fleshy; stipules free, scarious. Inflorescence a cyme, terminal. Flowers 5-merous. Pedicel reflexed, long. Sepals free, green, margin scarious. Petals white, margin entire. Stamens 10, rarely 5. Ovary 1-loculed, with numerous ovules; styles 5. Fruit a capsule, ovoid to subglobose, 5-valved, valves opposite sepals, many seeded. Seeds lenticular, often winged.
Five species: originally native to N temperate regions but now widespread as introductions; one species in China.
(Authors: Lu Dequan; Michael G. Gilbert)