Summary:
Features include 1) growth on conifer wood, either resupinate or more rarely bent out to form a dark brown cap projecting up to 1cm, 2) a spore-bearing surface that is cinnamon to dark brown and smooth, with a more or less distinct dark brown edge, 3) spores that cylindric to slightly allantoid, smooth, amyloid, and colorless, 4) cystidia that are thick-walled with the upper part strongly encrusted, and 5) a hyphal system that is dimitic (thin-walled colorless generative hyphae with clamp connections, and thick-walled brown skeletal hyphae). Amylostereum chailletii has been reported as transmitted and inoculated into dead trees by woodwasps (Sirex spp.): Amylostereum areolatum is a similar species confused with this species in the past, and since A. areolatum is known to be a symbiont with woodwasps, perhaps some of the North American reports of A. chailletii are in fact A. areolatum, (Ginns(5)).

Microscopic:
SPORES 5.5-7 x 2.5-3 microns, cylindric to slightly allantoid, smooth, amyloid, colorless; BASIDIA 4-spored, 33-45 x 4-5 microns, narrowly clavate, with basal clamp connection; CYSTIDIA 40-50 x 3-6 microns, conic, thick-walled, brownish, upper part strongly encrusted, a few thin-walled cystidia without encrustation, 120 x 5 microns; HYPHAE dimitic: generative hyphae 2-5 microns wide, thin-walled to thick-walled, some branched, septa with clamp connections, and skeletal hyphae 3-4 microns wide, thick-walled, brownish, (Breitenbach), SPORES 6-7.5 x 2.5-3 microns, cylindric or narrowly elliptic, smooth, amyloid; BASIDIA 4-spored, about 20-25 x 4-5 microns, narrow and clavate, with basal clamp connection; CYSTIDIA "yellowish brown, thickwalled and apically encrusted", the encrusted part about 15-20 x 5 microns, young cystidia "subulate, thinwalled and smooth", "A few larger, thinwalled, rounded to subulate cystidia often containing oily drops or resinous grains are seemingly of gloeocystidial character, and apparently remain thinwalled"; HYPHAE dimitic with thin-walled generative hyphae that have numerous clamp connections and thick-walled, straight, skeletal hyphae that are light brownish with few clamp connections: there are two distinct layers with different hyphal structures - a subicular or context layer with hyphae more or less parallel to the substrate (richly branched, colorless, clamped, generative hyphae and sparsely branched, straight, brown, skeletal hyphae), and a subhymenial layer with vertical hyphae (with mostly thin-walled to thick-walled generative hyphae 3-4 microns wide that enclose encrusted cystidia from previous hymenial levels), (Eriksson)

Notes:
A. chailletii has been found in BC, WA, OR, ID, AB, MB, NB, NF, NS, ON, PQ, AK, AZ, CA, CO, CT, IA, ME, MI, MT, NC, NH, NJ, NM, NY, PA, TN, VA, VT, and WI, (Ginns), Sweden (Eriksson), and Europe including Switzerland, Asia, (Breitenbach).

Synonyms and Alternate Names:
Hypoxylon punctatum (L.) Grev.
Poronia truncata (Bolton) Fr.