1. Zur Genetik und Cytologie von Oenothera ammophila Focke, Bauri Boedijn, Beckeri Renner, parviflora L., rubricaulis Klebahn, silesiaea Renner;Baerecke M. L.;Flora,1944
2. Twelve elementary species in Onagra;Bartlett H. H.;Greene, Cybele Columbiana,1914
3. Studies in Oenothera cytogenetics and phylogeny. Introduction and general summary;Cleland R. E.;Indiana Univ. Puhl. Sci. Ser.,1950
4. The nature and relationships of taxonomic entities in the North American Euoenotheras;Cleland R. E.;Indiana Univ. Puhl. Sci. Ser.,1950