What You Should Know
Panaeolus semiovatus is recognized by a viscid, cream-colored, wrinkled cap and annulate stipe.
Panaeolus semiovatus is also known as Anellaria Separata, is a medium-sized mushroom/toadstool that grows on horse dung, and has black spores. It is generally regarded as inedible, and a few people experience gastric upset after consumption.
The latter is distinguished by a rust-brown to the gray-brown, nonviscid cap, lack of annulus, and a partial veil that leaves fragments on the cap margin rather than a ring. Unrelated but somewhat similar in appearance to Panaeolus semiovatus is Volvariella speciosa. It also has a light-colored, viscid cap when moist, but doesn't occur on dung. Other differences include the presence of a volva, lack of an annulus, and salmon-pink spores.
Separating this Panaeolus from other members of the same genus is very straight forward because this is the only common member of the clan that has a stem ring. You need to look at young specimens because the ring is fragile and sometimes falls or washes off at maturity.
Other names: The Shiny Mottlegill, Egghead Mottlegill.
Panaeolus semiovatus Mushroom Identification
Saprobic; growing alone or gregariously on the dung of horses; spring, summer, and fall; widely distributed in North America.
3-9 cm; irregularly egg-shaped, becoming broadly conic or convex; slimy when fresh; often slightly wrinkled, but bald; whitish to pale tan; soft; the margin not lined; occasionally with hanging partial veil fragments.
Attached to the stem, or pulling away from it with maturity; close; whitish to grayish or brownish when young, but soon developing black areas and acquiring a mottled appearance; eventually black overall.
8-18 cm long; up to 1.5 cm thick; equal above a slightly enlarged base; smooth or powdery; whitish; with a high, thin ring that becomes blackened by spores and often disappears.
Black or blackish.
Questionable. (Arora: "edible according to most sources"; Jordan: "inedible"; McIlvaine: "excellent in substance and flavor"; Miller: "poisonous-hallucinogenic"; Phillips: "not edible"; Smith & Webber: "edible and good"; Stamets: "conflicting reports on the edibility of this species")
Spores 15-21 x 8-11 µ; smooth; more or less elliptical; often with a pore; dark brown in KOH. Pleurocystidia irregularly clavate, with refractive contents. Cheilocystidia absent or inconspicuous and basidiole-like. Pileipellis cellular/hymeniform, with pileocystidia.
Panaeolus semiovatus Taxonomy and Etymology
The basionym of this mushroom dates from 1798 when it was described scientifically by British naturalist James Sowerby (1757 - 1822), who gave it the binomial name Agaricus semiovatus. It was not until 1938 that the Egghead Mottlegill obtained its currently-accepted scientific name; that was when American mycologist Seth Lundell (1892 - 1966) transferred this species to the genus Panaeolus.
Synonyms of Panaeolus semiovatus include Agaricus separatus L., Agaricus ciliaris Bolton, Agaricus semiovatus Sowerby, Coprinus ciliatus (Bolton) Gray, Coprinus semiovatus (Sowerby) Gray, Panaeolus separatus L.) Gillet, Anellaria separata ( L.) P. Karst., Anellaria separata var. minor Sacc., Anellaria fimiputris, Panaeolus fimiputris, and Anellaria semiovata (Sowerby) A. Pearson & Dennis.
There is no consensus about the correct taxonomic position of fungi in the genera Panaeolus and Panaeolina, which some authorities include in the family Strophariaceae and others in the Bolbitiaceae.
The generic name Panaeolus means variegated - a reference to the mottling on the gills - while the specific epithet semiovatus means 'half an egg', so Egghead Mottlegill seems appropriate but perhaps Half-an-Egghead Mottlegill would have been even better.
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