Summary:
Diagnostic features include large size, a pale cap, fragile flesh when old, buff-colored decurrent gills, and a white spore deposit, (Arora). Other features include eventually funnel-shaped cap that is dry to moist but not hygrophanous, narrow gills, whitish to cap-colored stem, growth in woods or grassy areas, often in fairy rings or arcs, and elliptic, weakly amyloid spores. Sanchez-Garcia(1) say in 2014 that the current definition of Leucopaxillus "excludes species with smooth spores characterized by a weak amyloid reaction" and they place this species in Aspropaxillus. Vizzini(6) had shown a molecular separation between Aspropaxillus giganteus on one hand and Leucopaxillus albissimus and L. gentianeus on the other hand and they recombined Leucopaxillus septentrionalis into Aspropaxillus on the basis that previous authors considered them closely related morphologically. Aspropaxillus was originally described with Aspropaxillus giganteus as the type species to accommodate smooth-spored species with a clitocyboid habitus and a perisporium characterized by a weak amyloid reaction (according to Vizzini(6)).

Cap:
(5)8-35(45)cm across, large, convex becoming flat then broadly funnel-shaped, easily broken when mature, margin at first inrolled; white to buff or pale tan; smooth, not viscid, margin often obscurely ribbed when old^, (Arora), 5-39cm across, slightly convex soon becoming flat with margin that is downcurved and somewhat inrolled, becoming broadly funnel-shaped with arched margin; whitish to pale buff, disk darker buff; dry or moist but not hygrophanous, canescent (hoary) and rather unpolished, not striate, cuticle easily removed, (Bigelow), 10-45cm across, slightly convex to almost flat, rarely depressed from beginning, some becoming depressed with arched margin, finally funnel-shaped, never umbonate; creamy white, soon becoming darker especially in center, rarely with rusty brownish places; "slightly moist at first, drying quickly and not viscid", when young bald except for pubescent margin (surface with feel of kid-leather), later often more or less rimulose [finely cracked] or even faintly squamulose [finely scaly], especially in center, often grooved at margin, (Singer)

Flesh:
fragile when old; white^, (Arora), thick on disc, tapering gradually to margin, firm but pliant; whitish, (Bigelow), firm, finally soft in cap, watery in old specimens; white or whitish, (Singer)

Gills:
decurrent, close or crowded, at least some forked; pallid soon becoming pale buff, often pale dingy tan when old, (Arora), moderately decurrent to long decurrent, close or crowded, narrow, 0.5-1.3cm broad, frequently forking, not interveined; whitish, soon buff ("pale ochraceous buff" Ridgway(1) color), finally nearly alutaceous, (Bigelow), decurrent, crowded to very close, narrow, 5-13cm broad, anastomosing and sometimes forked, separable from cap, subgills "subsinuate, attenuate"; gills white or more often whitish with creamy or buffy tint, finally almost alutaceous; usually straight but sometimes crisped, (Singer)

Stem:
4-10cm x 2-4(6)cm, often stout, equal or widened slightly at either end; white, or when old pallid with darker fibrils, (Arora), (4.5)7-10cm x 2-6.5cm at top, equal or either end widened, central, solid, flattened at times; "generally whitish but fibrils darkening to pale grayish brown after handling"; longitudinally fibrillose-striate in upper part, "base somewhat embedded in substrate and with whitish tomentum", (Bigelow), 4.5-7.5cm x 2.2-5cm, solid, fibrous, "equal or irregular, occasionally ventricose or with an inflated base"; white to cap-colored; smooth or somewhat wrinkled when old, rarely split longitudinally, (Singer)

Odor:
pleasant to slightly disagreeable (Arora), rather pleasant and somewhat farinaceous, (Bigelow), weak, farinaceous or "mossy" according to Quelet, or "somewhat suggestive of skunk cabbage" according to Murrill, (Singer)

Taste:
pleasant to slightly disagreeable (Arora), mild or disagreeable, (Bigelow), mild (Singer)

Microscopic spores:
spores 6-8 x 3-4.5 microns, elliptic, smooth, weakly amyloid, (Arora), spores 6-8 x 3-4.5 microns, elliptic, smooth, amyloid; basidia 4-spored, 20-35 x (4.5)6-7(8) microns; [pleurocystidia and cheilocystidia presumably absent]; cap cutis of cylindric hyphae 3-6.5 microns wide; clamp connections present, (Bigelow), spores 5.3-8 x 3-5.7 microns, elliptic to oval, smooth, amyloid, mostly without oil droplet; basidia 4-spored, 35 x (5.5)6-6.5(8) microns; cheilocystidia none, (Singer)

Spore deposit:
white (Arora, Bigelow)

Notes:
Aspropaxillus giganteus has been found at least in WA, ID, MA, and TN, (Bigelow), AK (Miller), and WA, NY, France, and the USSR, (Singer). There are collections of Aspropaxillus giganteus from BC deposited at the University of British Columbia (as Leucopaxillus)

EDIBILITY

difficult to digest and poor in flavor, (Arora)

Synonyms and Alternate Names:
Leucopaxillus giganteus (Sowerby) Singer