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The Genus Agrocybe  

[ Basidiomycetes > Agaricales > Bolbitiaceae . . . ]

by Michael Kuo

The mushrooms in Agrocybe have brown spore prints and are small to medium-sized, saprobic species that grow in grass, wood chips, dung, garden mulch, or in woods--either terrestrially, or from deadwood. They are not subject to rapid decay (in contrast to the mushrooms in Bolbitius), and the caps, with a few exceptions, are dry. Unlike species of Conocybe, Agrocybe species have convex to flat caps.

In my area (central Illinois) May and June are the months for most Agrocybe species, and the little mushrooms proliferate in urban settings and along country roads in ditches and fields. There's no stopping them--but, after the first or second excited Agrocybe stop of the year, there's no stopping for me, either. The truth is, they're boring, and if you want to identify many of them with certainty you might as well get your javelin and head for the nearest windmill.

Why is Agrocybe identification a Quixotic effort? Because mating studies on the Agrocybe praecox cluster have already shown that the various species in the group can't be reliably separated with reference to their physical features (with or without a microscope), and because DNA studies have only just begun to address the species question in Agrocybe. In short, a lot of collecting and research needs to be done before we will have a clear picture of what the Agrocybe species are.

 

Agrocybe praecox

Agrocybe sp.

Agrocybe pediades


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Key to Agrocybe in North America


En Français (French translation by Roland Labbé).



1.Growing in clusters on wood (often the wood of willows or poplars); cap medium sized; stem with a sturdy ring; known from (and cultivated commercially in) Europe but also appearing in North America in southern hardwood forests or under baldcypress.
Agrocybe cylindracea
at Roger's Mushrooms
= Agrocybe aegerita

1.Not completely as above.
2


2.Partial veil present, sometimes forming a ring or ring zone, or leaving fragments on the cap margin.
3

2.Partial veil absent.
13


3.Cap dark brown in all stages of development; gills running down the stem.

3.Cap paler; gills attached to the stem or pulling away from it, but not running down it.
4


4.Growing in grass.
5

4.Growing elsewhere.
7


5.Stem only a few mm thick; cap small (1-3 cm), yellowish brown or paler; veil evidence very quickly disappearing; cap surface red or pinkish with KOH; spores 9-13 µ long.

5.Stem usually thicker and cap usually bigger than above; veil evidence fairly persistent on cap margin and/or stem; cap surface not red or pinkish with KOH; spores variously sized.
6


6.Cap white or very pale tan; most spores 10-14 µ long; clearly decomposing grass litter.
Agrocybe molesta
= Agrocybe dura

6.Cap usually darker than above; most spores 8-11 µ long; possibly decomposing buried wood (trees, woodchips, roots of former trees, etc. in the vicinity).


7.Mushroom identifier is willing to accept that recent investigations suggest the futility of determining subsequent Agrocybe species on the basis of morphology (physical features, assessed with and without a microscope).
8

7.Mushroom identifier likes old-school morphology, has a microscope, and doesn't care that the subsequent species, as currently defined, are probably invalid.
11


8.Growing in western North American forests in spring (account for elevation) under conifers or aspen; decomposing fragmented wood litter.
Flynn & Miller BS II
see Agrocybe praecox cluster

8.Not as above.
9


9.Growing in eastern North American hardwood forests (often with maples present); decomposing fragmented wood litter or growing from logs.
Flynn & Miller BS III
see Agrocybe praecox cluster

9.Not as above.
10


10.Growing in woodchips in urban settings across North America, or in disturbed ground (well worn paths, etc.) in spring.
Flynn & Miller BS I
see Agrocybe praecox cluster

10.Ecology not accounted for by choices above.


11.Stem 2-4 mm thick; growing in marshes and bogs; ring thin but persistent; spores 9-11 µ long; cystidia broadly fusoid-ventricose.

11.Stem thicker than above; habitat variable but not usually in marshes or bogs; ring persistent or not; microscopic characters variable.
12


12.Cap moist, dark yellowish brown when young, often wrinkled or veined near the center; ring persistent; cystidia clavate-mucronate, occasionally with fingerlike projections.

12.Cap dry, paler than above when young, the center not wrinkled or veined; ring sometimes collapsing or disappearing; cystidia utriform, without projections.


13.Growing in clusters on the dead wood of hardwoods; young cap dark brown.

13.Growing elsewhere; young cap not dark brown.
14


14.Taste bitter; growing on dung or in greenhouses.
Agrocybe amara

14.Taste mild or mealy; growing elsewhere. Note: Some of the subsequent species are morphological species unsupported by substantial ecological differences, and might easily collapse with mating and/or DNA studies.
15


15.Cap 5-10 cm wide; stem .5-1 cm thick; found east of the Great Plains.
Agrocybe sororia

15.Cap and stem smaller than above; variously distributed.
16


16.Stem with a long "root" or rhizomorphs attached to a fleshy underground mass (a sclerotium); gills distantly spaced; spores 8-10 x 4-5 µ; found in gardens.
Agrocybe arvalis

16.Not completely as above.
17


17.Cap pale, conspicuously wrinkled and pitted; found in lawns and grassy areas in subtropical and tropical areas; spores 15-17 x 7.5-9 µ.
Agrocybe retigera
at Agaricales of the Hawaiian Islands

17.Not completely as above.
18


18.Spores 7.5-9 x 5-6 µ; cap fleshy (about like Stropharia coronilla in thickness).
Agrocybe vervacti
(photos only)

18.Spores 9-13 (+) x 6.5-8 µ; cap thin.
Agrocybe pediades
(= A. semiorbicularis)



References

Flynn, T. & Miller, O. K. Jr. (1990). Biosystematics of Agrocybe molesta and sibling species allied to Agrocybe praecox in North America and Europe. Mycological Research 94: 1103-1110.

Gonzalez, P. & LaBarere, J. (1998). Sequence and secondary structure of the mitochondrial small-subunit rRNA V4, V6, and V9 domains reveal highly species-specific variations within the genus Agrocybe. Applied and Environmental Microbiology 64: 4149-4160.

Nauta, M. M. (2005). Agrocybe. In Noordeloos, M. E., Th. W. Kuyper & E. C. Vellinga, eds. Flora Agaricina Neerlandica: Critical monographs on families of agarics and boleti occurring in the Netherlands. Volume 6. Boca Raton: Taylor & Francis. 204-221.

Singer, R. (1977). Keys for the identification of the species of Agaricales I. Sydowia 30: 192-279+.



Cite this page as:

Kuo, M. (2006, September). The genus Agrocybe. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/agrocybe.html