A genus of about 14 species, wetland and aquatic herbs, primarily circumboreal in arctic and temperate regions, but also in the tropics of Asia, and temperate Australia.
Ref: Beal (1960); Cook & Nicholls (1986); Cook & Nicholls (1987); Crow & Hellquist (2000b); Ito et al. (2015); Kaul (2000) In Flora of North America Editorial Committee (2000); Kubitzki (1998b); Sulman et al. (2013); Thieret (1982). Show full citations.