Summary:
Features include 1) a viscid cap that is pale yellow with a slightly darker disc, becoming "Isabella color" to olivaceous in aging, the disk tinged orange at times, 2) close, broad gills that are whitish initially but soon violaceous brown, 3) a stem that is somewhat fibrillose to somewhat scaly below the membranous to fibrillose ragged fleeting ring, and 4) growth in moist areas under alder and Populus. Arora gives this as (=Stropharia magnivelaris?), but Smith, in his 1941 report of S. magnivelaris from Washington, pointed out that the veil was atypical for S. magnivelaris Peck, and in 1979 he placed these specimens in S. riparia Smith. The description is derived from Smith(18) except where indicated.

Gills:
broadly adnate and usually with decurrent tooth, becoming depressed around stem when mature, close, broad: 0.5-0.7cm; whitish when young, soon violaceous brown; edges even

Stem:
6-9(12)cm x 0.4-1(1.2)cm, equal or slightly widened in upper or lower part, hollow; white or whitish (pallid) but when old sordid brownish near base; somewhat fibrillose to somewhat scaly below ring, bald above

Veil:
ring submembranous [somewhat membranous] or merely fibrillose," whitish, usually very ragged and soon vanishing"

Microscopic spores:
spores 11-14(15) x 6-8 microns, elliptic to subovate, smooth, dark yellowish brown in KOH, truncate from apical to subapical germ pore; basidia 4-spored, 28-34 x 8-9 microns, colorless in KOH; pleurocystidia none, cheilocystidia "abundant and forming a sterile band on the gill edge", 20-40 x 4-7 microns, colorless in KOH, "clavate when young but soon filamentose and flexuous"; gill trama of interwoven hyphae 6-12 microns wide, colorless in KOH; cap cuticle a thin ixocutis; clamp connections present

Spore deposit:
[presumably near violaceous brown]

Notes:
It has been found in the Rocky Mountains and the Pacific Northwest including WA, (Smith(18)). It has been reported from BC (Kroeger(1)). There are collections from BC and OR at the University of British Columbia. There are collections from WA, AK, and CO at the University of Washington. It has also been found in California according to Desjardin(6), but says it is almost indistinguishable from the European Leratiomyces percevalii. According to Siegel(2) the common tan Leratiomyces found on wood chips in the Redwood Coast of California is Leratiomyces percevalii. Leratiomyces riparia was originally described from Washington. Although some collections at the University of British Columbia labeled as this species are probably Leratiomyces percevalii, collections from Meager Mountain (Pebble Creek) and Manning Park (Beaver Pond) would be this species with alders in riparian areas, (P. Kroeger, pers. comm.).

EDIBILITY

Synonyms and Alternate Names:
Stropharia riparia A.H. Sm.