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Scleroderma cepa

by Michael Kuo, 4 June 2025

Here is yet another earthball in the genus Scleroderma requiring microscopic analysis for confident identification. With a near-global distribution, Scleroderma cepa is widely encountered, appearing primarily under oaks in woodland settings, although it can also be found in parks and gardens near oak trees. The outer surface of Scleroderma cepa is relatively bald when young, but it often cracks up as the earthball matures. There is no pseudostem; instead, the earthball is attached to the substrate with a pinched basal area. Under the microscope, Scleroderma cepa has non-reticulate spores and lacks clamp connections.

Scleroderma laeve and Scleroderma albidum are nearly identical, differing primarily in spore dimensions. The latter has larger spores, 14–16 µm wide including ornamentation; the former has slightly larger spores (10–14 µm including ornamentation) and is associated with Eucalyptus in Africa, Oceania, and the Pacific Northwest of North America.

According to Guzmán (1970, 1985, 2013) Scleroderma flavidum is a synonym, representing a form that appears in beach sand, developing a pseudostipe-like mass of mycelium and rhizoids, and breaking apart into star-shaped rays.

Description:

Ecology: Mycorrhizal with oaks and other hardwoods; growing gregariously from spring through fall, or over winter in warm climates; originally described from France (Vaillant 1723); widely distributed in Europe and North America; reported from the Caribbean, Central America, South America, Africa, Oceania, and Asia. The illustrated and described collections are from Illinois and Ohio.

Fruiting Body: 1–5 cm across; more or less round; surface grayish brown to yellowish or brown, sometimes bruising yellow to pink or purple-red, relatively bald when young, becoming cracked and sub-scaly with age; skin 1–3 mm thick, white; spore mass white and fleshy at first, becoming gray to purplish black with whitish mottling and eventually powdery; with a pinched basal area but without a pseudostem; with white rhizomorphs attached to the base.

Odor: Not distinctive.

Chemical Reactions: KOH negative or red on surface.

Microscopic Features: Spores 7–10 µm excluding ornamentation; globose or subglobose; densely spiny with spines up to 1.5 µm long; not reticulate; golden brown in KOH. Clamp connections not found in peridial hyphae.

REFERENCES: C. H. Persoon, 1801. (Smith, 1951; Guzmán, 1970; Guzmán-Dávalos & Guzmán, 1985; Arora, 1986; Phillips, 1991/2005; Sims, Watling & Jeffries, 1995; McNeil, 2006; Trappe, Evans & Trappe, 2007; Buczacki et al., 2012; Guzmán et al., 2013; Desjardin, Wood & Stevens, 2015; Kibby, 2017; Jeppson, 2018; Læssøe & Petersen, 2019.) Herb. Kuo 09280501, 09300504, 10061202, 10122401.

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Spores

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Kuo, M. (2025, June). Scleroderma cepa. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/scleroderma_cepa.html