J. M.  Gillett and Robson, N. K. B., The St. John's-wort of Canada (Guttiferae). Ottawa: National Museums of Canada, 1981, p. iv, 40p.- illus., maps, chrom. nos., keys.

N. K. B.  Robson, ?Studies in the genus Hypericum L.  (Guttiferae).  2.  Characters of the genus.?, Bull. Brit. Mus. (Nat. Hist.), Bot., vol. 8, pp. 55-226, 1981.

N. K. B.  Robson, ?Hypericum specimens collected by Roy Lancaster in south-western China, October 1980.?, Int. Dendrol. Soc. Year Book, p. 141 (1980 publ. 1981) -, 1981.

N. K. B.  Robson, ?Studies in the genus Hypericum L. (Guttiferae): 2. Characters of the genus.?, Bull. Brit. Mus. (Nat. Hist.) Bot., vol. 8, pp. 55 - 226 (1981) - illus., chrom. nos., maps., 1981.