Lenzites betulina looks for all the world like Trametes versicolor or Trametes hirsuta, with its fuzzy, zoned cap. But flip it over and you will find that this little polypore has gills! We’re talking true gills here, not the maze-like or “nearly gill-like” pores of polypores like Daedaleopsis confragosa and similar mushrooms. If the notion of a polypore with gills strikes you as oxymoronic, I can’t argue with you–but see the essay below, “What, If Anything, Is a Gilled Mushroom?”
There are actually several “gilled polypores,” but distinguishing Lenzites betulina from the others is a fairly easy matter. It has stark white gills (when young and fresh), and white flesh, while the others–mostly in the genus Gloeophyllum–have darker gills and rusty brown flesh that turns black in KOH.
Ecology: Saprobic on the deadwood of hardwoods and, occasionally, conifers (originally named betulina by Fries, in Sweden, on the basis of its association with birch–demonstrated in Irene Andersson’s photo of the species in Sweden–but later discovered to be cosmopolitan in its host preferences); annual; growing alone or in overlapping clusters on logs and stumps; producing a white to straw-colored rot of the sapwood; summer and fall; widely distributed in North America.
Cap: Up to 10 cm across and 2 cm thick; semicircular, irregularly bracket-shaped, or kidney-shaped; flattened-convex; densely hairy, with concentric zones of texture; often radially bumpy or ridged; with zones of whitish, grayish, and brownish colors; flexible; without a stem; sometimes developing greenish colors in old age as a result of algae.
Gills: Whitish; well-spaced or fairly close; sharp; tough; up to 1 cm or more deep.
Flesh: White; extremely tough and corky.
Chemical Reactions: KOH negative on flesh.
Spore Print: White.
Microscopic Features: Spores 5-6 x 2-3 µ; smooth; cylindric; inamyloid. Cystidia absent. Hyphal system trimitic.