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..
In the genus Claudopus, recognized by some, the pileus is eccentric or lateral, that is, the stem is attached near the side of the cap, or the cap is sessile and attached by one side to the wood on which the plant is growing; or the plants are resupinate, that is, they may be spread over the surface of the wood.
The genus is perhaps not well separated from some of the species of Pleurotus with lilac spores like P. sapidus. In fact, a number of the species were formerly placed in Pleurotus, while others were placed in Crepidotus among the ochre-spored agarics. Several species are reported from America. Peck in 39th Report N. Y. State Mus., p. 67, et seq., 1886, describes five species.
Claudopus nidulans (Pers.) Pk. - This is one of the very pretty agarics growing on dead branches and trunks during the autumn, and is widely distributed. It has, however, been placed in the genus Pleurotus, as P. nidulans. But because of the pink color of the spores in mass, Peck places it in the genus Claudopus, where Fries suggested it should go if removed from Pleurotus. It seems to be identical with Panus dorsalis Bosc. It is usually sessile and attached to the side of dead branches, logs, etc., in a shelving manner, or sometimes it is resupinate.
The pileus is sessile, or sometimes narrowed at the base into a short stem, the caps often numerous and crowded together in an overlapping or imbricate manner. It is nearly orbicular, or reniform, and 1-5 cm. broad. The margin is at first involute. The surface is coarsely hairy or tomentose, or scaly toward the margin, of a rich yellow or buff color. It is soft, but rather tough in consistency. The gills are broad, orange yellow. The spores, pink in mass, are smooth, elongated, somewhat curved, 6-8 µ long.
Figure 144 is from plants (No. 2660, C. U. herbarium) collected in woods near Ithaca.