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Leucocoprinus cretaceus

[ Basidiomycota > Agaricales > Agaricaceae > Leucocoprinus . . . ]

by Michael Kuo

This little lepiotoid mushroom can be recognized by its powdery, pure white cap, its lined margin, and its habitat in cultivated areas, especially on woodchips. It vies with several species of Agrocybe for the title of "Rest Area Mushroom," since traveling amateur mushroomers frequently find it in woodchips surrounding the ever-present planted trees at interstate rest stops. Some people, who shall remain nameless, obviously don't know when to quit--although their traveling companions often do, and may be more than a little irritated when Leucocoprinus cretaceus decides a few hours later to go south instead of north, merrily decomposing in its sun-warmed, backseat paper bag.

Your North American field guide (including Mushrooms of the Midwest, 2014, by some guy named Michael Kuo and coauthor Andy Methven) may use the name Leucocoprinus cepaestipes (or "cepistipes") for Leucocoprinus cretaceus. File this under the "who knew?" category, but it turns out that the true Leucocoprinus cepaestipes features a brown cap center--even when young--and powdery scales that look different under the microscope (Vellinga, 2001e). Leucocoprinus cretaceus, in contrast, has a pure white white cap when young (although the center becomes yellowish to pale brownish with age); under the microscope its powdery scales are composed of funky, fat, sometimes cylindric, sometimes H- or Y-shaped, sometimes bone-like elements.

You want the truth? I have doubts about all of this. Buillard's original 1788 illustration clearly depicts a darkened cap center for Agaricus cretaceus, and the line between "pale tan center with old age" and "brownish center when young" seems pretty sketchy to me. Also, among my collections, anyway, the powdery scales on the cap surface are often composed of both cretaceus-like and cepaestipes-like elements, depending on where one sections the material and the age of the specimen, and identification winds up falling back on the pure-white-when-young thing. To my knowledge, no contemporary molecular study of this group has been published, but perhaps one will sort this mess out eventually.

Description:

Ecology: Saprobic; growing in groups or clusters in woodchips, cultivated soil, gardens, and so on (and occasionally in woods); summer; probably widely distributed in North America. The illustrated and described collections are from Illinois.

Cap: 3-7 cm; egg-shaped when young, expanding to broadly bell-shaped or nearly flat; dry; powdery with soft, white granules; usually becoming finely scaly over the center in age; white to beige when young, developing a slightly darker, yellowish or brownish center with age; the margin distinctly lined.

Gills: Free from the stem; close or nearly crowded; white, becoming pinkish and eventually brownish when past maturity.

Stem: 6-9 cm long; 3-6 mm thick; more or less equal above a somewhat swollen base; bald or, when young, dusted with white powder; whitish, developing pinkish hues; bruising slowly brownish; with a fragile, white, bracelet-like ring on the upper stem; basal mycelium white and copious; attached to white rhizomorphs.

Flesh: White; very thin.

Odor: Not distinctive.

Chemical Reactions: KOH negative on cap surface.

Spore Print: White.

Microscopic Features: Spores 7-10 x 5-6.5 µ; ellipsoid; smooth; hyaline to slightly yellowish in KOH; faintly to moderately dextrinoid; with a small pore; thick-walled. Cheilocystidia 50-75 x 10-20 µ; clavate to widely fusiform; with a short to long (5-20 µ) neck; hyaline; thin-walled. Pleurocystidia absent. Powdery material from cap surface with variable terminal cells that are cylindric to bone-shaped, H-shaped, Y-shaped, or irregular; flexuous, long, cylindric to subfusiform elements also sometimes present.

REFERENCES: (Buillard, 1788) Locquin, 1945. (Fries, 1821; Saccardo, 1887; Lincoff, 1992 ["cepaestipes"]; Metzler & Metzler, 1992 ["cepaestipes"]; Vellinga, 2001e; Vellinga, 2009; Kuo & Methven, 2014 ["cepistipes"].) Herb. Kuo 08230201, 08010302, 08160502, 08221402.

Lepiota cretacea is a synonym.


 

Leucocoprinus cretaceus

Leucocoprinus cretaceus

Leucocoprinus cretaceus

Leucocoprinus cretaceus

Leucocoprinus cretaceus
Spores

Leucocoprinus cretaceus
Cheilocystidia

Leucocoprinus cretaceus
Cap surface material: terminal cells



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Kuo, M. (2015, August). Leucocoprinus cretaceus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/leucocoprinus_cretaceus.html