The fungus frequently isolated from a destructive, brown, cubical rot in Sitka spruce and Douglas fir, and formerly referred to Trametes serialis Fries has been connected with a fruit body collected on Sitka spruce in the Queen Charlotte Islands, B.C. By means of morphological, cultural, and interfertility studies it has been shown to be distinct from Trametes serialis, and is described herewith under the name Poria microspora Overholts, n. sp. Similar studies of Poria Sequoiae Bonar, Polyporus palustris Berk., and Poria carbonica Over-holts n. sp., all of which have been confused with Trametes serialis because of similarities between fruit bodies or cultures, have demonstrated the validity of each of the species and have provided criteria for their separation on the basis of cultural characters.