A genus of about 225 species, perennial herbs, nearly cosmopolitan. Infrageneric classification (as clades) follows Huiet et al. (2018).
ID notes: Adiantum has sporangia borne marginally on the lower surface of the ultimate leaf segments, under a narrow false indusium (an often scarious flap). A distinctive feature is the black, dark purple or dark brown petiole and rachises, contrasting strongly with the pale green leaf segments. Most species of Adiantum in our region grow on or associated with rock outcrops, with the most widespread and northern species in the region, Adiantum pedatum, an exception, as it grows on rock outcrops or talus but also in mesic terrestrial situations away from exposed rock.
Ref: Huiet et al. (2018); Lin, Prado, & Gilbert in FoC (2013); Lu et al. (2011); Paris (1991); Paris (1993) In Flora of North America Editorial Committee (1993b); Tryon, Tryon, & Kramer In Kramer & Green (1990); Williams, Theis, & Hoess (2016); Zhao et al. (2021a). Show full citations.