E.  Haber, ?Variability, distribution and systematics of Pyrola picta s.l. (Ericaceae) in Western North America?, Syst. Bot., vol. 12, pp. 324 - 335, 1987.

H.  Takahashi, ?Pollen morphology and its taxonomic significance of the Monotropoideae (Ericaceae)?, Bot. Mag. (Tokyo), vol. 100, pp. 385 - 405, 1987.

G. D.  Wallace, ?Transfer of Eremotropa sciaphila to Monotropastrum (Ericaceae, Monotropoideae)?, Taxon, vol. 36, pp. 128 - 130, 1987.