Summary:
Features include a whitish, smooth cap, rather thick flesh, subdistant, broad, ventricose, white gills, a white, bald stem that widens downward to a swollen base, a coal tar odor, and microscopic characters. Tricholoma platyphyllum is not to be confused with Tricholomopsis platyphylla which is an alternate name for Megacollybia platyphylla. Tricholoma platyphyllum is similar to Tricholoma inamoenum and may be a synonym of that species according to Arora(1), Smith(14), and Trudell(4), but Leuthy(2) gives "white to yellow buff" cap for T. platyphyllum as opposed to "dingy white to pale yellow gray" for T. inamoenum, gills "white to light buff, on aging dark yellow" as opposed to "white sometimes blackening" and stem "whitish" as opposed to "whitish yellow, can [be] brown at base". Some people differentiate by more distant gills in T. platyphyllum (P. Kroeger, pers. comm.). The odor is the same. Smith says that if the European species (Tricholoma inamoenum) consistently has the small spores attributed to it by Lange(1) and Konrad and Maublanc (1928), Murrill''s species should be classed as a variety of it. Bessette(5) say T. inamoenum is thought by many to be the same as T. platyphyllum but "Murrill''s description makes no mention of odor, so accepting the synonymy seems premature as does applying the latter name to collections exhibiting the coal tar odor". The description is derived from Murrill(1) except where noted.

Cap:
3-5cm across, convex to slightly depressed; white with a cremeous tint; smooth, subglabrous [more or less bald], "margin entire, concolorous"

Flesh:
rather thick

Gills:
subdistant, very broad, ventricose; white, (Murrill), gills widely spaced (Arora), broad, distant, (Smith)

Stem:
8cm long and 0.5-0.9cm wide, widening downwards to swollen base; pure white, smooth, bald

Odor:
not mentioned in original description (Murrill), coal tar (Arora), like Tricholoma sulphureum (Smith)

Taste:
distinctive (Smith)

Microscopic spores:
spores 8.5 x 6 microns, (spores in holotype remeasured at 9-11(12) x 6-7.5(8) microns by Smith), elliptic, smooth, granular, colorless, (Murrill), spores 10-12 x 6.5-8 microns from deposits, turn yellowish-brown in iodine, (Smith)

Spore deposit:
[presumably whitish]

Notes:
The holotype is from WA. Tricholoma platyphyllum was found in WA and OR by Smith. There are collections from BC at the Pacific Forestry Centre and the University of British Columbia.

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