Trametes betulina (formerly Lenzites betulina), sometimes known by common names gilled polypore, birch mazegill or multicolor gill polypore, is a species of fungus.
Listed as uncertain.
Pileus horizontal, sessile, attached behind by an expanded base, more or less reniform or semicircular, tomentose or minutely velvety, pallid, slightly zoned, tinged brownish, becoming pale, margin similar in colour, 5-12 cm. long, 2.5-6 cm. broad; flesh up to 8 mm. thick behind, becoming gradually thinner up to the acute straight margin, corky and elastic, white; gills rather thin, radiating from the point of attachment of the fungus, broad, forked and anastomosing, straight, dingy-white; spores elliptical, smooth, 4 x 2 µ.
Notes: When young the gills are thickish, somewhat joined together here and there, resembling pores; at a later stage of development they become thin, with a thin sharp edge. Imbricated as a rule. Entire fungus corky and tough, firm and rigid, usually indistinctly zoned.