Macrocybe titans (probably)

[ Basidiomycetes > Agaricales > Tricholomataceae > Macrocybe . . . ]

by Michael Kuo

I wouldn't bet my life savings that the illustrated mushrooms are Macrocybe titans, but I'd be willing to put down a ten-spot. A reader in northern Florida sent the photos in a "What's This Mushroom?" e-mail, and my jaw dropped when I looked at the pictures. Look at the size of those things!

Believe it or not, there are a dozen or so gilled mushrooms that get this large, and I would need to study the mushrooms pretty carefully to be certain of an identification. But most of these huge agarics belong in the genus Macrocybe, which contains about seven species--and most of the seven can be ruled out as matches for the illustrated mushrooms. Macrocybe titans was originally described (as "Tricholoma titans") from grassy areas in northern Florida, a few counties away from where the illustrated mushrooms were growing.

Official descriptions of Macrocybe titans match the mushrooms in the pictures fairly well--but the defining features of the species are the presence of bent-back scales on the stem, and the presence of refractive pseudocystidia on the faces of the gills. As you can see, the stems are rather hard to see in the photos. I have not examined the mushrooms microscopically.

For a wonderful photo of verified Macrocybe titans specimens being sized up by mycologist Greg Mueller, see this page at the Field Museum's Web site. The stems of the mushrooms, which were growing in Costa Rica, are clearly scaly. According to Pegler and co-authors (1998), the Costa Rican version of Macrocybe titans is unique in that it grows "from active Atta ant gardens" (501) and has cystidia on the edges (as well as the faces) of its gills.

The edibility of Macrocybe titans is not known; I do not recommend experimenting.

Description:

Ecology: Apparently saprobic; growing alone or, more often, in clusters in grassy or sandy areas, or in ground disturbed by landscaping (usually in the year after the disturbance to the soil)--or, in Costa Rica, from ant colonies; fall and winter; tropical and subtropical in distribution.

Cap: 8-100 cm (that's up to one meter); convex, becoming broadly convex or flat; dry; smooth, but sometimes cracking in age like many of us; pale yellowish to buff, often with a pale cinnamon or yellowish center; fading with age to nearly white; the margin inrolled for quite some time.

Gills: Attached to the stem; very crowded; white to grayish or pale brown.

Stem: 6-35 cm long; 1.5-13 cm thick; equal or slightly swollen below (but never truly club-shaped); dry; whitish; with bent-back scales by maturity.

Flesh: White; firm; not changing on exposure.

Odor: Fragrant or not distinctive.

Spore Print: Creamy.

Microscopic Features: Spores 5.5-7 x 4-5 µ; smooth; vaguely oval or nearly round; inamyloid. Pseudocystidia scattered on gill faces; 35-50 x 7-10 µ; with refractive contents. Clamp connections present and conspicuous.

REFERENCES: (Bigelow & Kimbrough, 1980) Pegler, Lodge & Nakasone, 1998. (Bigelow & Kimbrough, 1980; Pegler, Lodge & Nakasone, 1998; Halling & Mueller, 2004.)

Tricholoma titans is a former name. Tricholoma cystidiosum of Mexico is a synonym.

Bigelow, H. E. & Kimbrough, J. W. (1980). Tricholoma titans, a new species from Florida. Mycotaxon 11: 425-429.

Pegler, D. N. et al. (1998). The pantropical genus Macrocybe gen. nov. Mycologia 90: 494-504.

Further Online Information:

Macrocybe titans at Macrofungi of Costa Rica

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Cite this page as:

Kuo, M. (2005, January). Macrocybe titans. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/macrocybe titans.html