A genus of about 10-20 species, annual herbs (or perennial by rooting at the nodes), of nearly cosmopolitan distribution in temperate regions.
Ref: Barger et al. (2023); Carolin In Kubitzki, Rohwer, & Bittrich (1993); Miller (2003b) In Flora of North America Editorial Committee (2003b); Schmidt (2023) In Weakley et al. (2023, in press). Show full citations.