A monotypic family, of temperate e. North America. In chemistry, morphology, and anatomy, Hydrastis shows some relationship to Podophyllum and Diphylleia of the Podophyllaceae (often included in the Berberidaceae). Though usually placed in the Ranunculaceae, Tobe & Keating (1985) present evidence from morphology, anatomy, embryology, palynology, chemistry, and cytology that suggests that Hydrastis is best recognized as a monotypic family. They contend that "Hydrastis represents a relictual primitive group which very early diverged from a common ancestral stock of the Ranunculaceae, Berberidaceae and probably of Circaeasteraceae, and that Hydrastis has evolved in its own evolutionary line parallel with other lines leading to the modern representatives of these families." Thorne (1992) and Reveal (1993a) have also accepted Hydrastidaceae as a distinct family. Tobe in Kubitzki & Bayer places Hydrastis with Glaucidium Siebold & Zuccarini in a bigeneric Hydrastidaceae. Zhai et al. (2019), like most recent authors, include Hydrastis in Ranunculaceae, but show Glaucidium and Hydrastis as successively basal in their broad Ranunculaceae, which is compatible with family rank recognition of these distinctive groups.
Ref: Reveal (1993a); Tamura In Kubitzki, Rohwer, & Bittrich (1993); Thorne (1992); Tobe (2003) In Kubitzki & Bayer (2003); Wang et al. (2009); Whittemore & Parfitt (1997) In Flora of North America Editorial Committee (1997); Zhai et al. (2019). Show full citations.