I. M.  Johnston, ?Studies in the Boraginaceae XI. 1. The species of Tournefortia and Messerschmidia in the Old World?, Journal of the Arnold Arboretum, vol. 16, pp. 145 - 168, 1935.

I. M.  Johnston, ?Studies in the Boraginaceae X. The Boraginaceae of Northeastern South America?, Journal of the Arnold Arboretum, vol. 16, pp. 1 - 64, 1935.