This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
This plant is not very common. It is often of quite large size, 6-15 cm. high, and the cap 5-10 cm. broad, the stem very short or sometimes long, from 1-2.5 cm. in thickness. The plant is quite easily recognized by the stout and black hairy stem, and the dark brown or blackish, irregular and sometimes lateral cap, with the margin incurved. It grows on wood, logs, stumps, etc., during late summer and autumn.
The pileus is convex, expanded, sometimes somewhat depressed, lateral, irregular, or sometimes with the stem nearly in the center, brownish or blackish, dry, sometimes with a brownish or blackish tomentum on the surface. The margin is inrolled and later incurved. The flesh is white, and the plant is tough. The gills are adnate, often decurrent on the stem, and easily separable from the pileus, forked at the base and sometimes reticulate, forming pores. Spores yellowish, oval, 4-6 x 3-4 µ. Stevenson says that the gills do not form pores like those of P. involutus, but Fig. 161 (No. 3362 C. U. herbarium) from plants collected at Ithaca, shows them well. There is, as it seems, some variation in this respect. The stem is solid, tough and elastic, curved or straight, covered with a dense black tomen-tum, sometimes with violet shades. On drying the plant becomes quite hard, and the gills blackish olive.
Paxillus atro-tomentosus, form hirsutus. Cap and stem brownish or blackish (natural size, small specimens, they are often larger). Copyright.