At the base of the stem, embedded in the substrate is a small reddish-brown sclerotium that somewhat resembles an apple seed.

C. tuberosa is found in Europe, North America, and Japan, growing in dense clusters on species of Lactarius and Russula, boletes, hydnums, and polypores.

tuberosus in his 1799 publication Observationes Mycologicae,[4] while Samuel Frederick Gray referred it to Gymnopus in 1821.

Molecular phylogenetic analysis reported in 2001 used RNA sequences to establish that C. tuberosa forms a monophyletic group with C. cookei and C. cirrhata;[2] this finding was later corroborated in a 2006 publication.

[14] The cap surface is dry to moist, smooth to covered with fine soft hairs, and somewhat hygrophanous—changing color depending on the level of hydration.

The top of the stem is covered with scales or a fine whitish powder, while the lower portion has hairs ranging from delicate to coarse.

The surface of the sclerotium is initially smooth, but later becomes wrinkled or furrowed; its interior is solid and white.

Their shape ranges from a contorted cylinder to roughly club-shaped to irregularly diverticulate (with short offshoots approximately at right angles to the main stem).

The cap cuticle is a thin layer of smooth thin-walled hyphae that are more or less radially oriented, bent-over, cylindric and somewhat gelatinous, measuring 2–5 μm in diameter; they are occasionally diverticulate.

The cuticle of the stem is made of a layer of parallel, vertically oriented smooth, thin-walled hyphae that are 2–4.2 μm in diameter, pale yellowish brown in alkali mounting solution.

[13] Baeospora myosura is similar in size and appearance to C. tuberosa, but grows on spruce and Douglas-fir cones.

[12] The two remaining Collybia species closely resemble C. tuberosa, but can be distinguished by examining the stem bases at the point of attachment into the substrate.

[19] A microscope provides a more definitive way of distinguishing the two: the hyphae in the sclerotia of C. cookei are rounded, while those of C. tuberosa are elongated; this diagnostic character is apparent with both fresh and dried material of the two species.

[17] Either way, the fruit bodies of the fungus are found growing solitarily or in dense clusters on the decomposing, often blackened remains of other mushrooms.

[13] In the Pacific Northwest region of the United States, Russula crassotunicata is a common and abundant species that has been definitively identified as a host of both C. tuberosa and Dendrocollybia racemosa.

[9] Collybia tuberosa is found in Europe and North America,[11] and in most common in the summer and autumn, coinciding with the fruiting periods of other mushrooms.