Summary:
Features include 1) resupinate growth on wood, 2) a broadly effused, thin, waxy-membranaceous fruitbody, loosely attached to the substrate, with a whitish, margin thinning out and fibrillose with some mycelial threads, 3) spores that are round, smooth, and inamyloid with a distinct apiculus, 4) (2)4-spored basidia, 5) projecting cystidia sometimes found that are capitate but not encrusted, and 6) hyphae with clamp connections.

Microscopic:
SPORES 4.5-6 microns in diameter, round, smooth; BASIDIA 4-spored, up to 6 microns wide; CYSTIDIA 4.5-6 microns wide, protruding about 30-50 microns beyond the basidia, often capitate and 6-9 microns wide at top, cystidia "not incrusted or with only a few incrusting granules"; no gloeocystidia; the compact hymenium supported by a very broad layer of hyphae 1.5-2 microns wide (rarely 3 microns wide), "loosely interwoven, thin-walled, granule-incrusted", "with the hyphae more densely arranged in the middle zone of this layer", (Burt), SPORES (5.5)6-6.5(7) microns, round, thin-walled to slightly thick-walled (up to 0.3 microns thick), with distinct apiculus; BASIDIA 18-33 x 6.5-8.5 microns, +/- clavate; LEPTOCYSTIDIA 40-50 x 6-7 microns, projecting up to 30 microns, the upper capitate part 7-8 microns wide, thin-walled, smooth, with basal clamp connection; HYPHAE 2-2.5(3) microns wide, colorless to slightly yellowish, thin-walled (up to 0.3 microns thick), (Julich(5)), SPORES (5.5)6-6.5(7) microns, colorless, inamyloid, with distinct apiculus, thin-walled to somewhat thick-walled (0.2-0.3 microns); BASIDIA mostly 4-spored, rarely 2-spored, 18-33 x 6.5-8.5 microns, clamped at base; CYSTIDIA relatively rare, not found immediately in all specimens, about 40-50 x 6-7 microns, projecting about 30-50 microns beyond the hymenium, capitate on the end (7-8 microns wide), thin-walled, colorless, with a large clamp connection at the base, not encrusted; hyphae about 2-2.5(3) microns wide, colorless to pale yellowish, walls thin to somewhat thick (about 0.3 microns), rarely anastomosing, clamp connections on all septa, crystals between the hyphae relatively frequent, (Julich(3))

Notes:
Athelia laxa has been found in BC, CT, PA, and VA, (Julich(3)).

Synonyms and Alternate Names:
Inonotus subiculosus (Peck) J. Erikss. & A. Strid.
Polyporus subiculosus Peck