This species has recently been illus- trated in field guides (Trudell and Ammirati 2009, p. 182; Siegel and Schwarz 2016, p. 132); many photographic re- cords on inaturalist.org and mushroomobserver.org may be correct, but have not been confirmed by sequence data.
Pileus 70–80(–300) mm or more in di- ameter, convex, reddish brown, paler on the disk, dry, minutely yellow fibrillose to subglabrous, even at the margin and appendiculate with fibrous veil remnants. Stipe 140–180 mm × 20–30 mm, strongly ventricose, larg- est below the middle, sometimes subradicating, pale brown, yellow fibrillose to subglabrous, white-mycelioid below, densely white-tomentose at the apex, annulate. Lamellae light brown, dark cinnamon in age, crowded, subsinuate, broad and subventricose, not marginate. Partial veil forming a flaring and persistent annulus, almost apical on the stipe. Flesh pale yellow, unchang- ing in colour, with a nondescript mushroom odour, bit- ter. (Adapted from Baker’s original field notes on the
MICROMORPHOLOGY (FIG. 16): Basidiospores (n = 285/4) amygdaliform, with conical apices, finely to coarsely roughened with irregular warts and ridges, darkening in 5% KOH, strongly dextrinoid, (6.6–)6.7–9.1(–10.2) um × (4.0–)4.3–5.2(–6.3) um (average = 7.9 ± 0.6 um × 5.2 ± 0.5 um), Q = (1.24–)1.31–1.72(–1.98) (average = 1.52 ± 0.1). Cheilocystidia (n = 84/4) mostly lageniform but with apex often slightly to moderately swollen and thus lecythiform; length = 22.4–42.5(–46.8) um, average = 32.5 ± 5.0 um; venter = (3.2–)4.4–8.9(–10.8) um, average = 6.7 ± 1.1 um; neck = (1.4–)1.7–3.7(–3.8) um, average = 2.7 ± 0.5 um; head = (2.2–)2.5–5.7(–5.8) um, average = 4.1 ± 0.8 um. Pleurocystidia (n = 14/2) scattered, similar to the cheilo- cystidia; length = 24.9–43.3(–45.9) um, average = 34.1 ± 4.6 um; venter = 5.9–9.8 um, average = 7.8 ± 1.0 um; neck = 0.8–5.2(–5.5) um, average = 3.0 ± 1.1 um; head = 2.6–6.7(– 7.0) um, average = 4.2 ± 1.3 um. Caulocystidia (n = 32/3) abundant above the annular zone, produced as terminal cells of long hair-like hyphae, narrowly ventricose- capitate to cylindric-capitate, sometimes cylindrical and without significant apical swelling; length = 41.0–73.3 um, average = 57.2 ± 8.1 um; venter = 2.0–7.7(–11.2) um, aver- age = 4.9 ± 1.5 um; neck = 1.4–4.8(–5.1) um, average = 3.1 ± 0.8 um; head = 2.5–7.3(–7.5) um, average = 4.9 ± 1.2 um. Basidia 4-spored, clavate to cylindrical, usually con- stricted near or above the middle, occasionally stipitate, 24.0–39.3 um × 6.4–8.6 um. Clamp connections present on nearly all septa.
ECOLOGY: Clustered on wood of coniferous trees.
COMMENTS: We do not have first-hand experience with this species in the field and have had to rely on literature reports for information on its appearance when fresh. It is characterized by its often large pilei, 30 cm or more in diameter (Trudell and Ammirati 2009; Siegel and Schwarz 2016), ventricose stipe, and occurrence on wood of conifers. It might be confused in the field with G. voitkii, which also grows on conifer wood but does not usually have a ventricose stipe. Microscopic examination is the most reliable way to distinguish the two species, as outlined in the key below.
Paul Stamets identifies a nom. prov. collection of G. ventricosus …
North American Species of Gymnopilus ….
A large west coast junonius-like species which likes conifer but occasionally occurs on hardwoods. Type location is Stanford, California. Original description: http://www.librifungorum.org/...