The genus Isopyrum was established by Linné in 1742. In Species Plantarum ed.
I: 557 (1753) he discriminated three species under this genus, i.e., Isopyrum fumarioides,
I. thalictroides and I. aquilegioides. The first was, however, separated by Reichenbach
as a monotypic genus-Leptopyrum in 1828, and according to Drummond & Hutchinson
the third species I. aquilegioides proved to be Aquilegia viscosa Gouan. Thus, the only
remaining species, I. thalictroides Linn. naturally constitutes the type of the genus Iso-
pyrum.
Since then, many new species had been discovered, some of which were later se-
parated as distinct genera by different authors. In 1920 Drummond & Hutchinson
published an elaborated revision of the genus Isopyrum, where, when recognizing Lepto-
pyrum, Souliea, Semiaquilegia as distinct genera, and also restoring the validity of
Enemion, they furthermore proposed two new genera: Asteropyrum and Paraquilegia.
In addition to the seven genera above mentioned, Ulbrich further established a new
genus Paropyrum in 1925, and another new genus Urophysa in 1929, basing on Iso-
pyrum anemonoides Kar. et Kir. (=Paraquiligia uniflora [Aitch.] Drumm. et Hutch.)
and I. henryi Oliv. (=Semiaquilegia henryi [Oliv.] Drumm. et Hutch.) respectively.
Our present study has shown that Asteropyrum, Paraquilegia, Leptopyrum, Semia-
quilegia, Souliea, Enemion, Usophysa are all remarkably distinct genera. As for genus
Urophysa, it reveals a very close affinity to Aquilegia in having stamanoides inside the
fertile stamens, the long-styled carpels and the similar nectariferous petals; but the
more simply divided leaves and the less conspicuous nectariferous organs seem to show
that the genus is more primitive than Aquilegia.
After a careful examination of the species of genus Isopyrum Linn. s.1. and of its
near allies, we find that I. thalictroides Linn., I. anemonoides Kar. et Kit. (=Paropyrum
anemonoides [Kar. et Kir.] Ulbr.) and I. manshuricum Kom. (=Semiaquilegia manshurica
Kom. and I. manshuricum Kom.) are homogenous both in habit and floral structure,
thus forming a very natural group. The genus Isopyrum Linn. itself, while remaining
sixteen species, however, form another natural group, which is easily distinguished from
Isopyrum by a series of important characteristics, for which we propose a new genus,
Dichocarpum. On account of the foregoing reasons, it is suggested that Paropyrum
Ulbr. will not uphold as a separate genus, and we also feel necessary to amend the cir-
cumscription of Isopyrum as construed by Drummond and Hutchinson.
