E-Flora BC: Electronic Atlas of the Flora of British Columbia

Summary:
Panaeolus semiovatus is recognized by a white to buff, viscid, parabolic to obtusely conic, smooth cap, gills that become mottled blackish, the presence of a ring, fruiting in dung especially of horses, and a blackish spore deposit. Panaeolus phalenarum (without a ring) is often considered a synonym. Anellaria was segregated from Panaeolus, but is not completely accepted. In the Pacific Northwest, it is more common east of the Cascade Mountains.

It has been reported from BC in Redhead(5), from CA and NM (Arora), and from YT (Miller(13)). Breitenbach(4) gave the distribution as Americas, Europe, Asia, North Africa, and Australia. There are collections at the University of British Columbia from BC. There are collections at the University of Washington from WA, OR, ID, AK, and MT.

Cap:
3-6(9)cm across, obtusely conic to parabolic, expanding to nearly convex; cinnamon buff becoming pinkish buff, fading to whitish; "viscid when moist, smooth to wrinkled", (Stamets), viscid when moist, often shiny when dry; margin sometimes hung with veil remnants, (Arora), deeply bell-shaped to obtusely conic; smooth, sometimes cracking, (Phillips)

Flesh:
relatively thick, soft; whitish, (Stamets), soft; pallid, (Arora)

Gills:
adnexed soon seceding, close to subdistant; pallid to brownish becoming mottled blackish, (Stamets), "adnate to adnexed or seceding; edges whitish, faces pallid becoming brown or grayish, then mottled with black, and finally entirely black", (Arora), free, crowded, narrow; pale gray then mottled black, (Phillips), notched (Lincoff(2))

Stem:
(8)10-16(18)cm x (0.4)0.6-1(1.2)cm, equal to slightly widened at base, solid becoming stuffed; whitish to pallid buff; striate to smooth and powdered, fragile membranous white ring radially striate from gills, (Stamets), equal or with enlarged base, stuffed or hollow; whitish to buff; top often striate, (Arora)

Veil:
partial veil leaving a fragile membranous white ring that is radially striate from gills, blackened by falling spores, (Stamets), small ring around center (Phillips), usually forming superior to median ring "but sometimes merely leaving a fibrillose zone", (Arora)

Odor:
not distinctive (Phillips)

Taste:
not distinctive (Phillips)

Microscopic spores:
spores 15-22 x 8-12 microns, elliptic to somewhat pip-shaped, smooth (Arora), spores 18.5-21.0 x 10-11.5 microns, elliptic, [smooth]; pleurocystidia of chrysocystidia type, 48-65 x 14-16 microns, ampullaceous, cheilocystidia 25-42 x 6-9(12) microns, variable in shape, fusoid-ventricose or pear-shaped or clavate, (Stamets), basidia 4-spored, 35-42 x 16-20 microns, clavate, with basal clamp connection; pleurocystidia developed as chrysocystidia, 30-45 x 20-25 microns, clavate, vesicular, or ventricose, cheilocystidia polymorphic, cylindric, ventricose, or forked, also clavate and some developed as chrysocystidia, 30-55 x 7-20 microns; clamp connections not seen on cap cuticle but present on basidia, (Breitenbach)

Spore deposit:
blackish (Stamets), purple-black (Buczacki)