Luebert, F., H. H.  Hilger, and M.  Weigend. 2011. ?Diversification in the Andes: Age and origins of South American Heliotropium lineages (Heliotropiaceae, Boraginales)?. Molecular Phylogenetics and Evolution 61(1):90 - 102. Retrieved  (http://dx.doi.org/10.1016/j.ympev.2011.06.001).