E-Flora BC: Electronic Atlas of the Flora of British Columbia

Agaricus diminutivus group
diminutive agaricus

Species account author: Ian Gibson.
Extracted from Matchmaker: Mushrooms of the Pacific Northwest.

Introduction to the Macrofungi

© Adolf Ceska  Email the photographer   (Photo ID #19188)

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Distribution of Agaricus diminutivus group
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Species Information

{See also Small Agaricus Table} Section Minores. Features of Agaricus diminutivus include small size, tall thin stature, pinkish brown to purplish fibrils on cap even at button stage, and conifer habitat. Phillips and Isaacs also say that it turns yellow, although this was apparently not noted by Peck. Kerrigan(1) calls it a flavescent species, and says that the stem becomes yellowish or orangish, and the stem flesh becomes yellowish, but says the cap flesh is unchanging and the cap becomes orangish on drying. The Kerrigan description below is from Kerrigan(1) but Kerrigan(3) generally follows the same description.

Phillips gives distribution as throughout most of North America. Isaacs(1) and Vellinga(5) record it for WA, and Kerrigan for CA. Oregon State University has collections from OR. University of British Columbia has a collection from BC by Pam Janszen. Hotson(1) described specimens from WA that Isaacs placed in a separate species Agaricus hotsoni with larger truncate spores (see separate entry), but that taxon was never validly published: the Hotson(1) description is included here for comparison.
1-3cm across, ovoid at first, later convex, finally nearly flat, not umbonate (in California collections, although one of Peck's description says "sometimes with slight umbo"); pink at first, when old becoming brown from appressed-fibrillose scales, disc concolorous, background whitish, becoming orangish on drying; dry, at first innately fibrillose, fibrils scant to absent near margin, when old forming pointed appressed-fibrillose fine scales about 0.05-0.1cm long and broad, (Kerrigan), 1-4cm across, "ovate then expanded-umbonate"; pinky-buff, darker in center, fibrils pinkish brown to purplish, cap bruising yellowish; dry, smooth to slightly fibrillose, (Phillips), margin incurved, (Chariton), 2.5-3.5cm across, shallowly bell-shaped, becoming flat, not umbonate, margin rounded, conspicuously exceeding gills by 0.2cm membranous extension; 'disc dark reddish brown, 7J10, outward "tilleul buff", R40, the vinaceous brown fibrils so sparse as to scarcely change the ground color', surface becoming intensely yellow where bruised; "dry, appressed-silky with innate, delicately streaked, widely spaced, aggregated fibrils", (Isaacs), 4cm across, convex or flat, with pink or rose-red scales on a grayish white surface, staining yellow where touched, (Hotson)
0.1-0.2cm thick; white, unchanging, in stem whitish becoming yellowish, (Kerrigan), 0.3cm off disc, soft; white, in stem white, turning yellowish when old, (Isaacs), thin, white, (Hotson)
free, close, up to 0.3cm broad; pallid then faintly if at all dull pink, finally dark blackish brown, (Kerrigan(1)), free, close, rather broad, about 0.5cm broad, narrowly rounded at stem, bluntly pointed toward margin; bright rosy pink, then grayish vinaceous, (color in unopened buttons not seen), (Isaacs), close, ventricose, moderately broad; soon becoming grayish or purplish gray then black; edges entire, (Hotson)
2-5cm x 0.1-0.3(0.4)cm, equal, narrowly stuffed-hollow, base shallowly rooted in forest litter; white, becoming yellowish or orangish; nearly bald in upper part, fibrillose in lower part when young, (Kerrigan(1)), 5-6cm x 0.4-0.5cm, equal, round in cross-section, base oval-bulbous, 1cm thick, stem narrowly stuffed, becoming hollow; pallid ivory, becoming ochraceous buffy downward when old, yellowish where bruised; bald above ring, sparsely floccose below ring, "often in obscure longitudinal patches", (Isaacs), 3-4cm x 0.3-0.4cm, equal, base slightly bulbous, stuffed then hollow; white, staining yellow where touched; satiny smooth, (Hotson), 2.0-6.0cm x 0.1-0.3cm (Desjardin)
ring small, fragile, pendant, flaring about 0.2cm, supramedian, white, not double, (Kerrigan(1)), ring superior, pendulous, 0.5cm wide, "persistent, thin-membranous, upper surface smooth, lower surface sparsely floccose, single, floccose edge", white or pale ivory, then apricot orange when old, (Isaacs), small, simple, superior, pendant ring, thin as tissue paper but persistent, white, (Hotson), ring white but becoming apricot-orange on drying or when old, (Chariton)
almonds (Kerrigan(1)), strong, pleasant, almond or anise, (Isaacs), pleasant (Phillips), none (Hotson)
pleasant (Phillips), none (Hotson)
Microscopic spores:
spores (4.1)4.9-5.4(6.4) x (3.4)3.6-3.9(4.5) microns, elliptic to broadly elliptic, dark brown, hilar appendix somewhat prominent, germ pore not evident; basidia 4-spored or substantially 2-spored, 10.5-20 x 7.5-10.5 microns, clavate to ventricose, sterigmata 2-4(6) microns long; cheilocystidia not observed, gill margin fertile; hyphae of annulus filled with orange inclusions when mounted in KOH (unlike Agaricus comptuloides), (Kerrigan(1)), spores 4.7-5.6 x 3.5-3.8(4.1) microns, obovate to elliptic in both face and side views, apiculus colorless, blunt, obscure, one to several droplets; basidia 4-spored, 15-21 x 6-8 microns, short-clavate with broad pedicel, colorless, sterigmata acuminate, about 2 microns long; cheilocystidia 8-21 x 6-8 microns, "short-clavate, broadly obpyriform, or sphaeropedunculate, often with a broad pedicel", the cells abundant, basidia-like, but broader in relation to length, not bright yellow in KOH, gill edge nearly sterile, (Isaacs), spores 4.5-5.5 x 3.5-5 microns, broadly elliptic, (Phillips), spores 6.5-7 x 4-5 microns, (Hotson(1))
Spore deposit:
deep brown (Phillips)

Habitat / Range

"scattered on soil and leaf litter", July to September, (Phillips), under conifers (Chariton), single to scattered-gregarious in litter of mixed evergreen and mixed coniferous forests, (Kerrigan(1) for California), gregarious under conifers in leaf mold and needles, (Isaacs), summer, fall

Taxonomic and Nomenclatural Links

Additional Range and Status Information Links


avoid because sometimes confused with Inocybes

Additional Photo Sources

Related Databases

Species References

Kerrigan(1)*, Kerrigan(3)*, Isaacs(1) (colors from Ridgway(1) and Kornerup(2) or Maerz(1)), Phillips(1)*, Arora(1), Barron(1)*, Chariton(1), Hotson(1), Vellinga(5), Desjardin(6)*, Siegel(2)*

References for the fungi

General References