I. M.  Johnston, ?Studies in the Boraginaceae 25. A revaluation of some genera of the Lithospermeae?, Journal of the Arnold Arboretum, vol. 3424. pp. 258 - 299, 1953.

I. M.  Johnston, ?Studies in the Boraginaceae 26. Further revaluations of the genera of the Lithospermeae?, Journal of the Arnold Arboretum, vol. 35, no. 1. p. 81, 1954.

I. M.  Johnston, ?Studies in the Boraginaceae 27. Some observations concerning the Lithospermeae?, Journal of the Arnold Arboretum, vol. 34. pp. 258 - 299, 1954.