Summary:
Features include 1) a chalky-white, slightly fleshy, innately silky-fibrillose cap, 2) white, notched-adnexed, close gills, 3) a short white stem that is equal above the somewhat abrupt bulb and is innately silky fibrillose, 4) growth in the first half of the year (in four collections), and 5) microscopic characters. Desjardin(6) says that this species has been called Inocybe geophylla in California, and that there are other species there that have gone under the name I. geophylla that may not include the real I. geophylla. They mention that an undescribed species is nearly indistinguishable from I. insinuata, and "forms more robust fruitbodies with a larger cap, broader stipe, and grows with oaks along the coast" [of California].

Cap:
3-5cm across, "subovoid, campanulate, finally convex-expanded, obtuse or broadly subumbonate", margin even; chalky white; "dry, innately silky-fibrillose"; slightly fleshy

Flesh:
white

Gills:
"sinuate-adnexed, narrow, close"; "whitish then pale-rusty-clay-colored", (Kauffman), "adnexed to adnate", 0.2-0.4cm broad, close with 2-3 tiers of subgills; "white to pale gray becoming dull brown", (Desjardin)

Stem:
2.5-4cm x 0.6-0.8cm, "equal above the subemarginate bulb, stuffed to hollow"; white; innately silky-fibrillose, (Kauffman), 2.0-5.0cm x 0.3-0.6cm, "cylindrical, sometimes subbulbous, solid"; white; dry, "apex pruinose, base fibrillose"

Veil:
"partial veil a thin, evanescent cortina, sometimes leaving fibrils on the cap margin" or top of stem, (Desjardin)

Odor:
spermatic (Desjardin)

Taste:
spermatic (Desjardin)

Microscopic spores:
spores 8-9 x 4.5-5 microns, smooth; "cystidia thin-walled, mostly slender, cylindric to subventricose above a slender pedicel, rarely elliptic and broad", colorless, scattered on sides of gills, more numerous on the gill edges, 55-65 x 8-15 microns, (Kauffman), spores 7.5-9 x 4.5-5.5 microns, elliptic, smooth; pleurocystidia, cheilocystidia, and caulocystidia (on stem apex) are all fusoid-ventricose and thick-walled; cap cuticle "a cutis of non-gelatinous to weakly gelatinous hyphae", (Desjardin)

Spore deposit:
dull brown (Desjardin)

Notes:
The University of Tennessee has two collections from BC and one from CA: it was described from CA. There are collections from BC also at the University of British Columbia.

EDIBILITY

unknown but presumed toxic (Desjardin)