S. V.  Meyen, ?Gymnosperms of the Angara Flora?, in Origin and evolution of the Gymnosperms, C. B.  Beck, Ed. New York: Columbia Univ. Press, 1988, pp. 338-381.

J. A.  Clement-Westerhof, ?Morphology and phylogeny of Palaeozoic conifers?, in Origin and evolution of the Gymnosperms, C. B.  Beck, Ed. New York: Columbia Univ. Press, 1988, pp. 298-337.