Lentil Shanklet

Appearance

The cap of ''C. tuberosa'' ranges in shape from obtusely convex to cushion-shaped with a margin curved inward when young, to flattened in age, with margin curved downward to straight. The cap sometimes has a shallow depression in the center, or a shallow umbo. Its diameter is small, reaching a maximum of 10 mm.

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. Sometimes the cap margin is pleated or grooved. The center of the cap is pinkish-buff but whitish around the margin, and it becomes whitish overall as it matures. The flesh is thin, and colored whitish to light buff. The mushroom has no distinctive taste or odor, and is considered inedible though nonpoisonous.

The gills are adnate , becoming subdecurrent with age . The gill spacing is close to subdistant, and the individual gills are whitish to pinkish-buff, thin, narrow to moderately broad, and have straight edges. The stem is 10–50 m long by 1–2 mm, and roughly equal in width throughout its length. It is slender and thread-like, flexible and pliant, with a dry surface. 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 color of the stem is generally whitish to pinkish-buff, but it darkens after it has been handled. The stem interior is pithy, and becomes hollow with age. The stems originate from a dark reddish-brown sclerotium of variable shape, typically measuring 3–12 mm by 2–5 mm. The surface of the sclerotium is initially smooth, but later becomes wrinkled or furrowed; its interior is solid and white.

It is often compared to an apple seed in appearance. Typically, several sclerotia are connected by thin strands of mycelia. The sclerotium is a resting structure that allows to fungus to overwinter in its host. In 1915, William Murrill reported the sclerotia of ''C. tuberosa'' to be bioluminescent.

The spore print is white. Individual spores are smooth, ellipsoid to tear-shaped in profile, obovoid to ellipsoid or cylindric in face or back view, with dimensions of 4.2–6.2 by 2.8–3.5μm. They are inamyloid and acyanophilous. The basidia are club-shaped to cylindric and 15.4–21 by 3.5–5 μm. The cheilocystidia are scattered to infrequent, inconspicuous, and 17.5–31.5 μm long. Their shape ranges from a contorted cylinder to roughly club-shaped to irregularly diverticulate.

There are no pleurocystidia. The gill tissue is made of interwoven hyphae that are non-reactive to Melzer's reagent. These hyphae are smooth and thin-walled, measuring 2.8–6.4 μm in diameter. The cap tissue is made of hyphae that is interwoven below the center of the cap, radially oriented over the gills, and inamyloid. These hyphae are smooth, thin-walled, and 2.8–7 μm in diameter.

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. The stem has moderately thin-walled and smooth cystidia that are resemble flexuous or contorted cylinders. They are hyaline in alkali, and 3.5–7 μm in diameter. Clamp connections are present in the hyphae of all tissues.

Distribution

It is not known if ''C. tuberosa'' is strictly parasitic, and needs the host to be living, or whether it is saprobic. 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. Hosts include agarics , boletes, hydnums, and polypores. 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''. The ''Russula'' fruit bodies are slow to decay, and are available nearly year-round as a substrate for the saprobes. Based on field observations, the authors suggest that ''C. tuberosa'' may produce fruit bodies on less decayed mushrooms, while ''D. racemosa'' produces them on much more heavily decayed mushrooms.

''Collybia tuberosa'' is found in Europe and North America, and in most common in the summer and autumn, coinciding with the fruiting periods of other mushrooms. It has also been reported from Japan.