A genus of about 80 species, annual and perennial herbs, nearly cosmopolitan, but primarily in temperate regions of the Northern Hemisphere.
Ref: Boufford (1997) In Flora of North America Editorial Committee (1997); Friis In Kubitzki, Rohwer, & Bittrich (1993); Grosse-Veldmann & Weigend (2017); Henning et al. (2014); Woodland (1982); Woodland et al. (1982). Show full citations.