Agaricus kriegeri

Description

Agaricus kriegeri is a brown mushroom with fibrillose scales on the cap. The fairly thick stem with a gradually swollen base. The rubbery ring with a thick edge. The flesh in the stem base may turn slightly yellow when sliced, or it may not.

Agaricus kriegeri has no legal synonym, although it has been confused in the past with other species. The “sp. K” thing was just a note on a voucher slip, to avoid launching an unintended provisional (illegal) name.

The “…placomyces sensu Krieger” indicates a misuse of a different name and, strictly speaking, is not a legal synonymous taxon. Presenting the alternate ID that way simply helps to clarify some older literature and (mis-)usage, for readers of today and tomorrow.

Mushroom Identification

1. Ecology

   Saprobic; growing gregariously under trees (including hemlocks, maples, and pines), usually in urban settings; summer and fall; possibly distributed throughout eastern North America.

2. Cap

   4–9 cm; convex or subconic at first, expanding to broadly convex; dry; when in the "button stage" covered with a fine, grayish brown, fibrillose covering that soon begins to be stretched into fibrillose scales; by maturity pale brownish underneath fine grayish brown scales that are more crowded over the center; the margin not lined, yellowing very slightly when rubbed repeatedly—or not yellowing.

3. Gills

   Free from the stem or nearly so; crowded; short gills frequent; pink, becoming brown and then dark brown in maturity; covered with a white partial veil when in the button stage.

4. Stem

   4–12 cm long; 1–2.5 cm thick; equal above a gradually swollen base; more or less bald; with a thick, rubbery, white ring that has a thickened, felty edge; whitish; bruising slightly yellow, or not bruising; basal mycelium white.

5. Flesh

   White; firm; unchanging when sliced, or becoming yellowish to yellow in the stem base.

6. Odor

   Phenolic, or not distinctive.

7. Chemical Reactions

   KOH yellow on cap surface.

8. Spore Print

   Dark brown.

9. Microscopic Features

   Spores: 5–7 x 3–4 µm; ellipsoid; smooth; thick-walled; brown in KOH, with a pale, contrasting apiculus; brown in Melzer's. Basidia 4-sterigmate. Cheilocystidia 20–32 x 8–12 µm; widely cylindric to sphaeropedunculate; smooth; thin-walled; hyaline in KOH; soon collapsing. Pleurocystidia not found. Pileipellis a cutis; elements 2.5–10 µm wide, smooth or slightly encrusted with pigment, brownish to golden brown in KOH.

Photo sources:

Photo 1 - Author: jenniferf4 (Attribution 4.0 Internationa)

Photo 2 - Author: cakewalk (CC BY-NC 4.0)