The Genus Scleroderma
[ Basidiomycetes >Boletales > Sclerodermataceae . . . ]
by Michael Kuo
Tough puffballs with blackish interiors, species of Scleroderma are sometimes called "earthballs" by field guide authors attempting to separate them from softer, fleshier puffballs. About 25 species of Scleroderma have been described world-wide, and most of these occur in North America. The easily recognized Scleroderma citrinum is well known and common, and famous for hosting the curious bolete Pseudoboletus parasiticus. In a bizarre turn of taxonomical events, recent DNA research has placed Scleroderma in the Boletales, with the boletes.
The two dozen species within the genus are separated primarily on the basis of microscopic analysis of their spores, and the principal monograph of the genus (Guzmán, 1970) is in Spanish, in a fairly obscure publication (does your library get Darwiniana?). All of this makes identification, outside of a few well known species, rather difficult for English-speaking amateur mushroomers. The key below is based in great part on Guzmán's monograph, and I have translated large parts of his descriptions in an attempt to make his wonderful insights more available to English-only readers. However, this makes for a rather "thick" key, filled with long descriptions. Additionally, I have organized the key according to macroscopic features whenever possible (including reactions to KOH). But the reader should be cautioned that Scleroderma species are often defined on the basis of their spores by mycologists, and most identifications should be seen as tentative unless confirmed with spore analysis.
For readers with microscopes, I have used the abbreviations A, B, and C in the key below to represent three general types of Scleroderma spores recognized by mycologists:
Key to 20 Scleroderma Species in North America
|1.||Outer skin usually thick (> 1 mm).|
|2.||Surface yellowish, covered with prominent, separated scales, dark reddish with KOH; without a pseudo-stem; growing in woods (often in mossy areas) or on well rotted wood east of the Rocky Mountains (more rare in the West and in Mexico); spores B/C, 11-14 µ.|
|3.||Mature mushroom large (9-13 cm across); without a pseudo-stem; surface red in KOH, covered with cottony mycelium when young but becoming smooth or irregularly and finely scaly; usually peeling open at maturity to dry out in a star shape (reminiscent of Geastrum); found in meadows and grassy areas (rarely in woods); spores B, 10-14 µ.|
|4.||Fresh surface bruising yellowish orange to reddish or reddish brown. (I enjoyed discovering that maltratar is Spanish-Mycologese for bruising; Guzmán's notation for Scleroderma michiganense, for example, is: "Poco se mancha de rojizo al maltratarse"--"Staining a little reddish when mistreated." Me too.)|
|4.||Fresh surface not bruising.|
|6.||Growing above ground under hardwoods, east of the Rocky Mountains in the United States; surface often scaly with small, flat or irregular scales; pseudo-stem usually present.|
|6.||Growing underground or partially underground under conifers in western North America and in montane Mexico; surface smooth; pseudo-stem usually absent.|
|7.||Primarily (but not exclusively) eastern in distribution; spores with narrow spines, 8-12 µ.|
|7.||Primarily (but not exclusively) southern in distribution; spores with blunt spines, 11-16 µ.|
|8.||Surface prominently scaly or spiny at maturity.|
|8.||Surface smooth, wrinkled, or somewhat scaly when mature--but not prominently scaly or spiny.|
|9.||Surface with pyramid-shaped spines up to 1.5 mm high; mushroom small (to 3 cm across) and reddish brown; KOH reaction unknown; tropical and subtropical in distribution; spores B, 7-9 µ.|
|9.||Surface conspicuously scaly with flat or nearly pyramid-shaped scales up to 2 mm high or more; mushroom sometimes larger than above (1-7 cm across); KOH yellowish to reddish; found in the southeastern United States and the mountains of Mexico; spores A, 8-12 µ.|
|10.||With a pseudo-stem accounting for almost half of the mushroom's height (Sims et al.)--or shorter (Guzmán); growing in sand on the Atlantic Coast of the United States (but also recorded in Michigan, California, and the Bermudas); surface yellowish brown with reddish tints at maturity; usually peeling open at maturity to dry out in a star shape (reminiscent of Geastrum); KOH brown on dried herbarium specimens (fresh reaction not recorded); spores B, 9-12 µ.|
|11.||Recorded from the western United States, often in sandy soil; with a sturdy, often twisted or ribbed pseudo-stem attached to rhizomorphs; surface smooth at first, becoming scaly near the apex (sometimes becoming cracked, with reddish tints in the cracks), whitish to straw-colored; spores A, 9-11 µ.|
|11.||Recorded from California and Michigan in arid, disturbed ground; with a short, wrinkled pseudo-stem attached to rhizomorphs; surface smooth at first, becoming scaly near the apex (sometimes becoming cracked, with reddish tints in the cracks), dark yellowish or yellowish brown; spores B, 11-16 µ.|
|12.||Found in sandy soil (sometimes on woody debris) in tropical regions; surface smooth at first, becoming scaly near the apex, brownish above and yellow below, not bruising; inner surface of skin bright sulfur yellow; with a short, poorly defined pseudo-stem with yellow rhizomorphs; KOH reaction not recorded; spores B, 7-9 µ.|
|13.||Fresh, young surface not bruising reddish; distribution tropical.|
|13.||Fresh, young surface bruising reddish; variously distributed.|
|14.||Peeling open at maturity to dry out in a star shape (reminiscent of Geastrum); surface whitish to straw-colored, smooth to finely scaly or covered with cottony fibers; growing in sand dunes and sandy areas in the Caribbean and Florida; spores B, 5-8 µ.|
|14.||At maturity developing a small star-shaped pore at the apex (through which spore dust escapes); surface brownish yellow to dark brown or grayish, with small and irregular dark scales; growing in various habitats in the Caribbean; spores C, 10-13 µ.|
|15.||Growing in sand dunes or sandy areas in the United States; with a well-defined, underground base or pseudo-stem (5-10 cm long) composed of bundled rhizomorphs; surface mottled yellowish, smooth or with irregular scales, dark reddish brown in KOH; spores C, 8-16 µ.|
|16.||Surface scaly (at least at the apex) by maturity, with dark scales creating a "leopard skin" effect over a pale yellowish background; spore dispersal through a single pore that develops at the apex; spores A.|
|16.||Surface smooth to finely scaly at maturity but not appearing like leopard skin; spore dispersal through various apical cracks; spores C.|
|17.||Widely distributed in North America on soil or humus (sometimes on rotting wood) in forests, open areas, gardens, and moist, shaded areas; KOH instantly yellowish brown or dark red on surface; pseudo-stem only rarely present; spores 11-15 µ, with spines up to 2 µ long.|
|17.||Primarily tropical and subtropical in distribution, often in oak woods; KOH slowly brownish on surface; pseudo-stem frequently present, 1-4 cm long; spores 8-13 µ, with spines up to 1 µ long.|
|18.||Growing in open areas or in hardwood forests; surface dark reddish with KOH, developing dark reddish cracks.|
|18.||Growing under conifers; surface reaction to KOH not recorded, not typically developing reddish cracks.|
Binder, M. & Bresinsky, A. (2002). Derivation of a polymorphic lineage of Gasteromycetes from boletoid anscestors. Mycologia 94: 85–98.
Coker, W. C. & Couch, J. N. (1928). The Gasteromycetes of the Eastern United States and Canada. Chapel Hill: University of North Carolina Press. Reprinted by Dover Publications, 1974.
Guzmán, G. (1970). Monografía del género Scleroderma Pers. emend. Fr. (Fungi - Basidiomycetes). Darwiniana 16: 233–401.
Guzmán, G. & Ovrebo, C. L. (2000). New observations on sclerodermataceous fungi. Mycologia 92: 174–179.
Sims, K. P., Watling, R. & Jeffries, P. (1995). A revised key to the genus Scleroderma. Mycotaxon 56: 403–420.
Smith, A. H. (1951). Puffballs and their allies in Michigan. Ann Arbor: University of Michigan Press. 131 p.
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Cite this page as:
Kuo, M. (2011, July). The genus Scleroderma. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/scleroderma.html