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Summary: The distinguishing feature is growth from a small, black, easily overlooked tuber, but even without that, it is easily recognized in the field by a broadly convex cap that soon becomes flattened, long, slender, minutely pubescent stem, lack of a veil, bitter taste, and (microscopically) remarkable digitate pleurocystidia. The description from Hansen is for A. arvalis (Fr.) Heim & Romagn. A. arvalis as interpreted by Singer in the 1936-1950 period is different and now referred to as Agrocybe subpediades (Murrill) Watling.
Agrocybe arvalis is rare. It was reported from BC by Redhead(16). Breitenbach(4) give the distribution as Europe and Asia.
Cap: 1-2cm across, convex becoming flat, sometimes depressed at center or with shallow umbo; pale ochraceous or buff with or without distinct cinnamon tinge, drying deep ochraceous, expallent [? becoming pale on drying]; smooth to slightly rugulose [wrinkled], but strongly wrinkled when dry, "greasy when moist, matt when dry", margin membranous, hardly or not striate, (Watling), 1.5-2.5cm across, convex; yellow-brownish to ocher-brownish often pale, (Moser), up to 2.5cm across, "ochraceous brownish with yellowish cast, paler when dry", (Courtecuisse), 1-3.5cm across, deep yellow to ochraceous, (Hansen)
Flesh: buff in cap, paler in stem, (Watling)
Gills: slightly adnate, fairly broad; "buff when young, then tinged cinnamon and finally brick", (Watling), narrow; brown, (Moser), broadly adnate, not very close; brownish to warm tobacco brown, (Courtecuisse)
Stem: 5-12.5cm x 0.2-0.4cm, equal or widening slightly downward, tough to elastic, stuffed, narrowing below soil surface into a rooting base or mycelial root, "or attached to a blackish brown sclerotium up to the size of a large pea"; ivory to pale buff at top, darker below; pruinose throughout, (Watling), with +/- well developed mycelial root originating in black sclerotium, (Moser), up to 10cm long and up to 0.5cm wide, rooting, often arising from black sclerotium (which can be as large as a chickpea), (Courtecuisse), 5-10(15)cm x 0.2-0.5cm, rooting, usually (always?) springing from a black 2-3(5)cm large sclerotium; stem pale yellowish; pulverulent [powdery], (Hansen)
Microscopic spores: spores 9-10 x 5-6 microns, elliptic in face view, only slightly flattened on one side in side view, dull fulvous in water and alkali, germ pore small; basidia 4-spored, 25-30 x 5-7.5 microns, cylindric-clavate; pleurocystidia club-shaped or with 2-5 finger-shaped, upright, apical appendages, 45-60 x 10-15 microns (including appendages), neck 4-5 microns broad, cheilocystidia 35-50 x 7-10 microns, cylindric or subulate to lageniform, colorless; cap cuticle a hymeniform layer of vesiculose cells, 20-35 x 8-10 microns, "intermixed with lageniform or subfusiform cystidia"; stem cuticle of parallel hyphae bearing caulocystidia 50-100 x 7-10 microns, lageniform to fusiform; clamp connections present, (Watling), spores 9-12 x 5-6 microns, pleurocystidia with finger-like extensions, (Moser), spores 9-12 x 4.5-6 microns; pleurocystidia digitate, cheilocystidia lageniform to subfusoid, (Hansen), spores 8.6-11 x 4.6-5.8 microns, elliptic, smooth, pale honey-brown, thick-walled, with small germ pore up to about 1 micron across; basidia 4-spored, 25-30 x 6-7 microns, cylindric, some with basal clamp connection; cheilocystidia 35-55 x 6-15 microns, lageniform to subulate, pleurocystidia ventricose, with 3-5 digitiform outgrowths apically, 60-80 x 15-20 microns including the outgrowths; no clamp connections seen on cap cuticle, (Breitenbach)
Spore deposit: snuff brown (Watling), tobacco brown (Breitenbach)
Habitat / Range
"on the ground in fields, copses and open woodland" (Watling for Britain), fields and meadows (Moser for Europe), tracks, fields, meadows, (Courtecuisse for Europe), amongst grass in pastures, in stubble fields, on roadsides and in gardens, (Hansen for Europe), spring, summer, fall (Buczacki)
See also SIMILAR section of Agrocybe semiorbicularis and Hypholoma tuberosum.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2020. E-Flora BC:
Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for
Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2023-09-25 12:23:43 AM
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