Calvatia fragilis

[ Basidiomycota > Agaricales > Agaricaceae > Calvatia . . . ]

by Michael Kuo

Calvatia fragilis is essentially a smaller version of the well-known Calvatia cyathiformis. Like that species, it has purple-brown spore dust at maturity and, under the microscope, it features spiny spores. Calvatia fragilis differs, however, in its smaller size and in the fact that it lacks a substantial sterile base section.

Some mycologists treat Calvatia fragilis as a mere form of Calvatia cyathiformis (officially, "Calvatia cyathiformis f. fragilis")—a position possibly supported by my collecting experience; several times I have collected the two "species" within a few feet of each other. However, I admit I have never found specimens that appear to "intergrade" between cyathiformis and fragilis; for this reason I am treating the taxa as separate species. I am unaware of any contemporary, DNA-based studies addressing the issue.

Description:

Ecology: Saprobic; terrestrial; growing alone, gregariously, or in fairy rings in grass—on lawns, in meadows, and so on; summer and early fall; widely distributed in North America. The illustrated and described collections are from Illinois and Québec.

Fruiting Body: Shaped like a ball, or nearly so; 2–8 cm across and 2–4 cm high; whitish to gray or pale grayish brown, or purplish in places; with age the surface usually developing a mosaic pattern; outer "skin" about 1 mm thick; interior flesh white, becoming yellow to yellowish and eventually turning into purple-brown spore dust; basal area lacking or extremely rudimentary (and then composed of cottony fibers).

Odor and Taste: Not distinctive.

Chemical Reactions: KOH negative on surface.

Microscopic Features: Spores 4–5.5 µm (measured without ornamentation); globose or subglobose; densely spiny with spines 1–1.5 µm long; hyaline in KOH. Capillitial threads 2–10 µm wide; thick-walled; septate; hyaline in KOH.

REFERENCES: (Quélet, 1886) Morgan, 1890. (Saccardo, 1888; Coker & Couch, 1928; Smith, 1951; Zeller & Smith, 1964; Smith, Smith & Weber, 1981; Kreisel, 1994; Desjardin, Wood & Stevens, 2015; Seigel & Schwarz, 2016.) Herb. Kuo 10310701, 07120803.

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Spores and capillitial thread

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Kuo, M. (2017, September). Calvatia fragilis. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/calvatia_fragilis.html