Description from Flora of China
Herbs annual. Stems slender, branched. Leaves petiolate, subopposite; ocrea membranous. Inflorescence paniculate. Flowers bisexual. Perianth 3(-5)-parted. Stamens 3, alternate with tepals and 3 glandlike staminoids. Ovary ovoid, compressed; styles 2, persistent, very short; stigmas capitate. Achenes narrowly ovoid, biconvex.
About three species: Arctic regions, Asia, N Europe, North America; one species in China.
(Authors: Li Anjen (李安仁 Li An-ren); Alisa E. Grabovskaya-Borodina)