Cap 4.0-13.0 cm broad, hemispherical in youth, expanding to plano-convex, with or without a low umbo; margin at first incurved, fringed, becoming decurved, sometimes upturned in age; surface fibrillose to squamulose, the ornamentation pallid to greyish-brown, if the latter, darkest at the disc; context thick, white, tinged greyish-tan near the cuticle; odor and taste strongly fungal.
Gills free, crowded, cream-colored, unchanging when bruised; lamellulae in four to five series.
Stipe 5.0-10.0 cm long, 1.5-2.5 cm thick, often stout, stuffed to hollow, equal, spindle-shaped to clavate, the base pointed and typically well buried in the substrate; surface white with appressed fibrils, slowly brownish where handled; partial veil fibrillose-membranous, white, the edge blunt, colored like the cap margin, forming a medial to superior annulus, or absent when left as fragments on the young cap.
Spores 6.5-8.5 x 4.0-5.0 µm, smooth, oval to elliptical in face-view, similar in profile, but slightly inequilateral, germ pore lacking, dextrinoid; spore print cream.
Solitary or in small groups, in sparse grass, along paths, and roadsides; fruiting in late summer in watered areas and after the fall rains; said to occur commonly in agricultural fields in the Pacific Northwest; infrequent in the San Francisco Bay Area.
Edible, according to the literature.
Leucoagaricus barssii bears a resemblance to a more common cousin Leucoagaricus leucothites (= L. naucinus), but differs in having a fibrillose, often shaggy appearing cap, a usually more robust stature, and typically rooted stipe. Habitat preference also separates the two species, Leucoagaricus barssii occurring on drier sites, e.g. sandy soils with sparse grass as opposed to well-watered lawns. Interestingly, in the Pacific Northwest where Leucoagaricus barssii is more common and grows larger, it is found in moister settings, i.e. agricultural fields and around compost heaps. Look-alikes of Leucoagaricus barssii include Agaricus species, two of which are mildly toxic, Agaricus xanthodermus and Agaricus californicus. They can be distinguished by their blackish-brown gills at maturity, and tendency to yellow and smell of phenol when bruised.