A genus of about 40 species, nearly cosmopolitan. Classification of subgenera and sections follows Ito et al. (2017).
ID notes: Counts of leaf-teeth do not include the broadened, sheathing base of the leaf. Seeds are necessary for the identification of most species.
Ref: Bräuchler (2015); Crow & Hellquist (2000a); Fernald (1902); Freeman & Pfingsten (2021); Haynes (1979); Haynes (2000c) In Flora of North America Editorial Committee (2000); Haynes & Hellquist (1996); Haynes, Holm-Nielsen, & Les In Kubitzki (1998b); Ito et al. (2017); Les et al. (2015); Rüegg et al. (2017). Show full citations.