A genus of about 82 species, herbs and shrubs, cosmopolitan.
ID notes:Many natural hybrids are known. Hybrids are generally recognizable from their intermediate morphology and usual association with their two parents. However some hybrids resemble one parent much more than the other, and some hybrids are found in populations independent (and even disjunct) from one or both parents. Allopolyploidy may have had a major role in the evolution of this genus, especially section Microcarpium, which has a majority of polyploid species.
Ref: Duke (1955); Eyde (1977); Eyde (1978); Eyde (1981); Harper (1904a); Hoch (2021a) In Flora of North America Editorial Committee (2021); Munz (1944); Munz (1965); Nesom & Kartesz (2000); Peng (1984); Peng (1986); Peng (1988); Peng (1989); Peng & Tobe (1987); Raven (1963); Raven & Tai (1979); Wagner, Hoch, & Raven (2007); Ward (2001); Ward (2012a); Zardini, Gu, & Raven (1991). Show full citations.