Summary:
Features include soft fragile texture; viscid, yellow, striate cap; rust-colored gills when old; and rusty orange to rusty brown spore deposit. Breitenbach(4) give the opinion that Bolbitius reticulatus (Pers.: Fr.) Ricken with a lilac, reticulate-venose cap, Bolbitius lacteus J.E. Lange with a white cap, and B. variicolor G.F. Atk., with an olive-yellow to olive-brown, sometimes venose cap, are not separate species but only deviations from the type of Bolbitius vitellinus caused by substrate, age, or weather, especially since the microscopic characters do not show any marked differences. [Note that Bolbitius lacteus J.E. Lange is also considered by some a synonym of Conocybe albipes Hauskn.] The online Species Fungorum, accessed February 21, 2012, gives the current name of B. variicolor G.F. Atk. as Bolbitius titubans var. olivaceus (Gillet) Arnolds.

Cap:
1.5-7cm across when expanded, oval to conic or bell-shaped when young, often becoming flat when old; "bright yellow to pale yellow (the center sometimes yellow-orange)", but often fading when old or as it dries to whitish, brownish, grayish, etc.; smooth, viscid or slimy when moist, margin striate, at times conspicuously grooved nearly to center, (Arora), 1-5cm across, bell-shaped at first or convex, then broadly convex, often retaining small central umbo, infrequently flat-convex, rarely becoming depressed; bright lemon chrome or luteous, on expanding retaining the color throughout although more strongly at center, "or becoming cinnamon or saffron towards margin"; "viscid from separable pellicle, margin faintly striate at first but often becoming fisso-sulcate", (Watling)

Flesh:
thin, soft; yellowish, (Arora)

Gills:
"adnate to adnexed or free, close, soft, dissolving somewhat in wet weather"; "pallid or pale yellow to pale brown", becoming rusty ocher to cinnamon brown when old, (Arora), "free or almost so, soon separating, thin, papery, rather narrow", "at maturity tending to collapse but not autodigesting"; "straw at first then tinged rust and finally deep rusty tawny", (Watling)

Stem:
(3)5-12cm x 0.2-0.8(1)cm, equal or widening in lower part, "hollow, very fragile when thin (readily collapsing)"; whitish to pale yellow; often delicately pruinose or scurfy, (Arora), 3-6cm x 0.2-0.5(0.7)cm, slightly swollen downward, hollow; white or pale lemon yellow or flushed with cap color; minutely flocculose throughout especially toward the top, (Watling)

Veil:
absent (Arora), veil remnants not seen (Watling)

Odor:
indistinct (Watling)

Taste:
indistinct (Watling)

Microscopic spores:
spores 10-16 x 6-9 microns, elliptic, smooth, truncate from large apical germ pore, (Arora); spores 12-13(15) x 6-7 microns, elliptic in face view, slightly flattened on one side in side view, sienna in water, rich rusty tawny in alkali, germ pore large and prominent; basidia 4-spored, 20-30 x 10-15 microns, colorless, clavate; pleurocystidia rare, when present lageniform, pavement cells prominent, cheilocystidia variable, utriform or lageniform with long or short neck, intermixed with a few colorless inflated cells, 30-50 x 14-20 microns; cap cuticle a hymeniform layer of vesiculose, colorless, smooth, pedicellate cells filled with yellow juice, 25-50 x 10-15 microns, embedded in thick, gelatinized layer intermixed with detritus; stem cuticle of cylindric hyphae clothed in groups of colorless, elongate-clavate to lageniform cells; clamp connections not seen, (Watling)

Spore deposit:
rusty orange to rusty brown (Arora), sienna [an ocher brown] to rust, (Watling)

Notes:
Bolbitius vitellinus is commonly found on foray lists from the Pacific Northwest including BC. There are collections at Oregon State University from OR. It is reported from ID by Andrew Parker, pers. comm. It is found in CA (Desjardin). Breitenbach(4) give distribution as North America, Europe, Asia, and North Africa.

EDIBILITY

yes, flavorless, (Arora)

Synonyms and Alternate Names:
Bolbitius vitellinus (Pers.) Fr.
Bolbitius vitellinus var. olivaceus Gillet