Diminutive Agaricus

Description

Diminutive Agaricus is a common, small, gilled mushroom. It occurs in the United States and southern Canada east of the Great Plains and on the West Coast. It is found in summer and fall, alone, widely scattered, or in small groups, in woodlands, especially coniferous woodlands, and in pastures. The handful of records from Minnesota range from mid-June to early September.

Agaricus diminutivus is part of a group or complex of species or forms that are difficult to tell apart. The tall thin stature, the brown gills, the ring on the stalk, the cap and stalk staining yellow when bruised, and especially the small size, are the defining features of the group.

When it first appears, the cap is ovoid or convex, and white or cream colored, sometimes with a slight yellowish or buff tone. There are usually purplish brown or pinkish brown, flattened or appressed, hair-like fibers (fibrils) in the center, which become scarce at the margins, even at this early stage. As it matures the cap expands. The mature cap is ⅜″ to 1½″ (1 to 4 cm) in diameter, convex, broadly convex above and flat below (plano-convex), or almost flat and slightly raised in the center (umbonate). The background color is whitish, cream, or pale tan, sometimes with a slight yellowish or buff tone. It is usually darker in the center due to a concentration of minute, appressed fibrils that are individually too small to be discerned by the naked eye. The cap stains yellow when bruised.

The gills are pinkish at first, becoming reddish brown, then chocolate brown or dark brown as the spores mature. They are closely spaced, and they are not attached to the stalk (free) at maturity.

The stalk is ¾″ to 2¾″ (2 to 7 cm) long, and 1⁄16″ to ¼″ (2 to 6 mm) thick. It is white at first, usually becoming yellowish or orangish. At or above the middle there is a ring of tissue, a remnant of the partial veil, the veil that covers the developing gills when young. It is a drooping, “skirt-like ring” at first, but it is fragile and it soon drops away, leaving a washer-like “intermediate ring” on the stem. Like the cap, the stalk stains yellow when bruised.

The flesh is thin and white. It does not stain when bruised or sliced. It is edible but not recommended. It is too small to be worth collecting for the table, and it can easily be confused with other species, like Inocybe, some of which are poisonous.

The spore print is chocolate brown.

Similar Species

Habitat and Hosts

Woodlands, especially coniferous woodlands, and pastures

Ecology

Season

June through September in Minnesota