2 literature references:

Author: Kreczetowicz, V.I.
Year: 1941
Title:
Source: In:Flora URSS, Vol.11. Mosqua, Leningrad. (Rus)
Author: Komarov,V.L.
Year: 1945
Title:
Source: Flora of the U.S.S.R. Vol XI (Engl. Translation 1972)