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Agaricus porphyrocephalus

by Michael Kuo, 8 September 2024

Agaricus porphyrocephalus is a brownish, fibrillose version of "Agaricus campestris," known from lawns and meadows in eastern North America. It features gills that are pink before turning brown, non-staining flesh, a flimsy ring, and relatively small spores. Despite appearances, however, Agaricus porphyrocephalus is not particularly closely related to species in the campestris group; its ITS sequences clearly separate it.

A white variety, Agaricus porphyrocephalus var. pallidus, is very similar in appearance to the campestris group species, and is best separated from them on the basis of its smaller spores. I have collected the two varieties growing within a few yards of each other.

Thanks to Andy Methven for documenting, collecting, and preserving Agaricus porphyrocephalus for study; his collection is deposited in The Herbarium of Michael Kuo.

Description:

Ecology: Saprobic; growing alone, scattered, or gregariously in meadows, fields, lawns, and grassy areas; fall; originally described from Denmark (Møller 1952); widespread in Europe and in North America east of the Great plains. The illustrated and described collections are from Illinois, New Jersey, and North Carolina.

Cap: 2.5–9 cm; convex, becoming broadly convex, with or without a central hump; dry; whitish to brownish underneath brown to grayish brown fibrils and scales; the young margin often adorned with hanging whitish remnants of the partial veil.

Gills: Free from the stem; close or crowded; short-gills frequent; whitish in buttons but soon pink, then maturing to dark brown; covered with a thin white partial veil when in the button stage.

Stem: 2.5–6 cm long; 1–1.5 cm thick; more or less equal above a slightly tapered base; with a quickly collapsing whitish ring; whitish to brownish; bald or finely fibrillose.

Flesh: Whitish; not changing when sliced.

Odor and Taste: Not distinctive.

Chemical Reactions: KOH negative on cap surface.

Spore Print: Dark brown.

Microscopic Features: Spores 5.5–7 x 3.5–4.5 µm; ellipsoid; smooth; thick-walled; brown in KOH. Basidia 20–25 x 4–6 µm; clavate; 4-sterigmate. Pleurocystidia not found. Cheilocystidia not found. Pileipellis a cutis; elements 5–10 µm wide, smooth, hyaline to yellowish or brownish in KOH.


REFERENCES: F.H. Møller, 1952. (Moser, 1978; Phillips, 1981; Cappelli, 1984; Weber & Smith, 1985; Phillips, 1991/2005; Hansen & Knudsen, 1992; Nauta, 2001; McNeil, 2006; Buczacki et al., 2012; Kuo & Methven, 2014; Kerrigan, 2016; Knudsen et al., 2018; Kibby, 2021.) Herb. Kuo 10030503, 10101515, 05162402.


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Agaricus porphyrocephalus

Agaricus porphyrocephalus

Agaricus porphyrocephalus

Agaricus porphyrocephalus

Agaricus porphyrocephalus

Agaricus porphyrocephalus

Agaricus porphyrocephalus

Agaricus porphyrocephalus
Spores



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Kuo, M. (2024, September). Agaricus porphyrocephalus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/agaricus_porphyrocephalus.html