2 literature references for Trifolium nigrescens (Clementi)Holmboe:

Author: Heywood,V.H. & Ball,P.W.
Year: 1968
Title:
Source: Leguminosae.In:Flora Europaea Vol.2.ed.Tutin,T.G.et al.
Author: Holmboe,J.
Year: 1914
Title:
Source: Stud.Veg.Cyprus