Collybia tuberosa, commonly known as the Lentil Shanklet, is a small, whitish agaric with a thin cap and a slender stem that arises from a hard, reddish-brown sclerotium resembling an apple seed. The mushroom is typically found growing in dense clusters on decaying remains of other fleshy fungi, particularly Russula and Lactarius species. It favours damp woodland habitats, where the remnants of these host mushrooms provide the necessary substrate for its growth.

Cap very small, convex with an inrolled margin when young, becoming broadly convex to flat, sometimes with a slight central depression. The surface is smooth, dry to moist, whitish to pale buff, occasionally with a faint pinkish or brownish tinge near the centre. The flesh is whitish and extremely thin. Gills attached to the stem, close to almost distant, whitish to pale pinkish, narrow. Stem very slender, equal or slightly tapering, whitish to pinkish and becoming hollow with age. The base is attached to a small, reddish-brown, tear-shaped or elliptical sclerotium resembling an apple seed. The stem has no ring. Spore print white.

Microscopic Features: Spores are 4–6 × 3–3.5 µm, smooth, ellipsoid to sublacrymoid, and inamyloid.

Collybia tuberosa on the www.first-nature.com web site.
Collybia tuberosa on the MushroomExpert.Com Web site.