Summary:
Postia leucomallella forms a small, narrow. elongated cap along the upper edge of its decurrent tube layer. Microscopically there are usually light yellow gloeocystidia in the hymenium. The current name in the online Species Fungorum, accessed April 20, 2020, is Fuscopostia leucomallella, but the current name in Mycobank, accessed the same day, is Postia leucomallella. The description is derived from Gilbertson(1).

Taste:
bitter (Ginns(28), p193)

Microscopic:
spores 4.5-6 x 1-1.7 microns, allantoid [curved sausage-shaped], smooth, inamyloid, colorless, thin-walled; basidia 4-spored, 12-18 x 4-6.4 microns, clavate, with basal clamp; gloeocystidia "rare to abundant, apparently in some cases lacking completely", arising in subhymenium, mostly embedded, rarely projecting, 10-35 x 4-8 microns, cylindric to clavate and obtuse, colorless, thin-walled; hyphae monomitic, generative hyphae with clamp connections, colorless and 2-4.5 microns wide, "those of the subhymenium more narrow than those of the context, thin-walled to slightly thick-walled and with conspicuous clamps"

Notes:
Postia leucomallella has been found in ID, MI, MN, NY, and PA (Gilbertson). In BC it is known only from one collection (Ginns(28)).

Synonyms and Alternate Names:
Leccinum testaceoscabrum (Secr.) Singer