How to tell Split fibrecap from Deadly fibrecap

The cap is 3-10 cm across, hemispherical to convex in young mushrooms, with a broad umbo in the center; it opens out with age. The surface is silky-shiny, with fine radial fibers and flattened scales. At first the color is whitish, cream or ivory; with age and when touched it slowly turns red — first pinkish, then brick-carmine or cinnamon-red. The reddening is most visible along the cap margin and wherever the mushroom is damaged. This is the key diagnostic feature.

Cap 2-7 cm across; in young mushrooms conical or bell-shaped with a pointed knob, later it opens out, but the knob stays. Color yellowish-ochre, straw-yellow, light brown in old mushrooms. The surface has a distinctive radially fibrous pattern, and when mature — deep radial cracks from the center to the edge (hence the species name rimosum — "cracked"). The margin is often split and upturned.

Gilled hymenophore. The gills are fairly crowded, notched where they meet the stem. In young mushrooms they are whitish-pinkish, with age olive-brown to brick-brown. The spore print is olive-brown or tobacco-colored — typical of the whole genus Inocybe.

Gilled hymenophore. Gills fairly crowded, notched where they meet the stem. In young mushrooms they are whitish-gray, turning olive-brown or tobacco-colored with age. Spore print tobacco-brown or tobacco-colored — typical of the whole genus Inocybe.

The stem is 3-10 cm tall and 0.5-1.5 cm thick, cylindrical or slightly widening toward the base. It's whitish to cream, with a pink or reddish-brick tinge (especially in the lower part). When touched and with age it turns red, just like the cap. The surface is lengthwise-fibrous, with no ring. The flesh of the stem is firm.

Stem 3-8 cm tall, 0.4-1 cm thick, cylindrical, even or slightly thickened toward the base. Whitish to yellowish, paler at the top. Surface lengthwise fibrous, no ring. Flesh of the stem firm, hollow in old mushrooms.

The flesh is thick and white; when cut, it slowly turns red (not right away: sometimes only after 30 minutes or more), especially in the lower part of the stem. This is an important way to tell it from most Agaricus mushrooms, whose flesh either doesn't change color or turns yellow (though some wood mushrooms, such as Agaricus silvaticus, also redden, so check the gills and spore print too). The smell and taste of the fresh flesh are pleasant, fruity and sweetish — which is exactly what makes it so treacherous.

Flesh thin, whitish to yellowish, does not change color when cut.

Sweet and fruity, with notes of ripe pears or apples — unusual for the genus Inocybe, which usually smells spermatic or musty. This appealing aroma + a reddening white cap + the season when edible white mushrooms are being picked = the perfect trap for a beginner forager. Never rely on smell when identifying this species.

Distinctly spermatic or stale and musty — typical of the whole genus Inocybe. This is an important diagnostic sign: if an unknown brownish mushroom has this unpleasant smell, throw it away without hesitation. Some sources describe the smell as "stale flour". The taste is mild or slightly bitter — do NOT rely on taste.