Caps shell shaped, joint and superimposed like the tiles on a roof; blackish violaceous, brownish, or grayish ochraceous; fading to yellowish with age; margin rolled toward the gills; then explanate and undulate; cuticle smooth, but with glittering granules in the variety glandulosus; lucid, but slightly velvety near the stem; diameter of a single cap 5-15 cm, diameter of the tuft 15-35 cm. Stems lateral, slanted, sometimes rudimental; but very long in the variety stipitatus; with pubescent bases confluent in a single mass; stuffed, firm, white, smooth. Flesh thick, tender, then tough; white. Odor agreeable. Flavor sapid. Gills more or less close; broad; decurrent on the stem through a thread; not crossing one another; white or cream; also with shiny granules in the variety glandulosus. Spores white, tinged with amethystine. It grows in tufts, in autumn, until the first winter rigors, but also in winter when this is mild, on trunks and stumps of latifoliate trees, rarely on conifers. Edible, of good quality and very much in demand. On the other hand, the variety columbinus is edible only with caution, since it can cause diarrhea and other intestinal trouble, particularly in delicate individuals; cap reddish ocher, reddish at the center, blue violaceous at the margin; then green or blue green; sometimes entirely blue; growing on latifoliate trees but more often on conifers.