C. L.  Lundell, ?Studies of American plants - I?, Wrightia, vol. 4, pp. 97-128, 1969.

B.  Maguire, Wurdack, J. J., and Allen, C. K., ?The botany of the Guayana Highland - Part V?, Memoirs of the New York Botanical Garden, vol. 10, no. 5, pp. 1-278 [44-123 by C.K. Allen], 1964.