Isopyrum.

When circumscribed (as here) to include Enemion, a genus of about 9 species, perennial herbs, of temperate North America and temperate e. Asia. The issue of the separation of the genus Enemion from Isopyrum has remained controversial and uncertain since the 1960s, though most authors treated the two as separate following papers in the 1960s through 1990s (see, for instance, Keener 1977, Tamura 1993, and Ford 1997). Recent phylogenetic results of Ling et al. (2024) make the separation of Enemion and Isopyrum very problematic, with members of the two genera forming a strongly supported monophyletic clade, but each genus not supported as monophyletic (for instance, "Enemion biternatum" is sister to Isopyrum thalictroides and Isopyrum manshuricum). We here include Enemion Rafinesque (1820) in Isopyrum Linnaeus (1753) based on the preponderance of evidence.

ID notes: Isopyrum biternatum is somewhat superficially similar to the more common and widespread (in the Flora area) Thalictrum thalictroides, with which it also sometimes grows, but can be distinguished by the following characters: stem leaves 1-4 and alternate (vs. stem leaves 2 and opposite), fruit an aggregate of follicles (vs. fruit an aggregate of achenes), petaloid sepals 5 (vs. 5-10, usually some at least of the flowers on a plant with 6 or more), leaflets deeply lobed, at least some of the leaflets on a plant with sinuses at least 1/3 as long as the leaflet (vs. leaflets shallowly lobed, the notches < 2 mm long).

References: Ford (1997g) In Flora of North America Editorial Committee (1997); Tamura (1993) In Kubitzki, Rohwer, & Bittrich (1993). Show full citations.

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