Full name: Hebeloma fragilius (Peck) Sacc. (1887)
Published: Syll. Fung. 5: 798 (1887)
Taxonomic status: We have not been able to unambiguously determine the current genus of this name.
Basionym: Agaricus fragilior Peck [as "Agaricus (Hebeloma) fragilior"] (1875)

Types: UNITED STATES: New York: Hamilton County, Indian Lake (approx. 43.7824°N, 74.2654°W, alt. approx. 500 m a.s.l.) on boggy soil and litter in bog, Jul. 1873, C.H. Peck (Holotype. herbarium acc. no. NYS-F-001238, HJB1000271).

The type material is a mixed collection.

Diagnosis: Small, fragile, pale grayish ochre; pileus thin, convex, then expanded or centrally depressed, sometimes irregular or wavy on the margin, at first minutely squamulose lamellae close, when young a little paler thin the pileus, minutely eroded on the edge; stem slender, squamulose, hollow, often expanded at the base into a thin disk. Plant about ???? pileus 3-6" broad stem scarcely 1" thick. Damp. decaying leaves in water holes of swamps. Indian Lake. July. The minute scales of the pileus easily rub off and they disappear with age. They sometimes project from the margin in a fimbriate manner.

Commentary: This taxon was originally described by Peck (1875) as Agaricus (Hebeloma) fragilior. The exsiccata that was examined was very small. Unfortunately, no molecular information was forthcoming. The spores that were found were near hyaline, pip-shaped, very weakly ornamented, and measured around 7 × 5 μm. The protologue describes the mushroom as small and fragile with a thin grayish ochre pileus with minute scales that easily rub off. In an unpublished manuscript Hesler on North American species of Hebeloma gave the following description: “The pileus cuticle is a zone of dry cells, and the surface bears inflated pileocystidia which at intervals loosen, push up, and form erect scales. The spores are 6.5–7.5(8) × 4–4.5 μ[m], without a germ-pore, minutely rugulose, thin-walled, and are faintly yellowish in 2% KOH. It appears to be an Alnicola. Peck (1910) thought it might be a Naucoria and that it needed further study. It may also have some affinity to Tubaria.” The only conclusion is that this is not a Hebeloma, but on the information available, we are not able to unambiguously assign this species to any genus.