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Scleroderma citrinum

by Michael Kuo, 30 June 2025

This well-known species of Scleroderma, as it is currently defined, has a near-global distribution. It was originally described in association with European oaks (Persoon 1801), as a tough earthball with a yellowish to yellowish brown, prominently scaly outer surface. By maturity the scales are fairly large, well separated, and brownish, contrasting with the paler base color.

Slice open Scleroderma citrinum when fresh and young to see its white outer rind, measuring 1–3 mm thick (and possibly blushing yellowish to reddish after slicing), as well as the purple-gray to purple-black, mottled interior. With maturity the solid interior turns into a powdery, blackish to dark brown mass of spore dust.

Under the microscope, Scleroderma citrinum features spores that are usually reticulate—but, contrary to what is widely repeated in many sources, the reticulation is sometimes partial or even absent. In the collections I have examined this variation has been the case, even within a single specimen, lending support to the conclusion drawn by Sims et al. (1995) that "[t]he spore ornamentation of this species seems to vary greatly between sub-reticulate or catenulate spores, to mildly or strongly reticulate spores."

Scleroderma citrinum is the only mushroom that plays host to Pseudoboletus parasiticus, an extremely odd little bolete that actually parasitizes the earthball. See the linked page for illustrations.

Thanks to Michelle Lierl for documenting, collecting, and preserving Scleroderma citrinum for study; her collection is deposited in The Herbarium of Michael Kuo.

Scleroderma aurantium and Scleroderma vulgare are synonyms.

Description:

Ecology: Mycorrhizal with oaks and other hardwoods but often found in mixed woods (I find it most often in eastern hemlock woods where oaks are scattered); often found in mossy areas, and occasionally on well-rotted wood; growing alone, scattered, or gregariously; summer and fall, or over winter in warm climates; originally described from Europe (Persoon 1801); widely distributed in Europe and North America; also reported from the Caribbean, Central America, South America, Oceania, Asia, and Africa. The described and illustrated collections are from Indiana, Kentucky, Michigan, and North Carolina.

Fruiting Body: 2–5 cm across; spherical or a little flattened; surface hard and scaly, yellowish to yellow-brown, often cracked, when fresh usually bruising yellowish to pinkish or red; scales well separated, large, darker than ground color; rind 1–3 mm thick, whitish, when sliced usually blushing yellowish or reddish; spore mass at first hard and purplish gray to purple-black, mottled with whitish areas—becoming blackish to dark brown and powdery; usually without a pseudostem, but pinched at the point of attachment; base attached to whitish to yellowish rhizomorphs.

Odor: Not distinctive.

Chemical Reactions: KOH red to brownish red on surface.

Microscopic Features: Spores 7–11 µm excluding ornamentation; globose or subglobose; densely spiny with spines 1–1.5 µm long and scattered to frequent connecting ridges; usually reticulate but sometimes only partially so, and occasionally merely spiny; dirty golden brown in KOH. Peridial hyphae 4–15 µm wide; smooth; walls 1.0 µm thick; hyaline in KOH; conspicuously clamped.

REFERENCES: C. H. Persoon, 1801. (Smith, 1949 & 1951 as "aurantium"; Guzmán, 1970; Phillips, 1981; Smith, Smith & Weber, 1981; Arora, 1986; Breitenbach & Kränzlin, 1986; Phillips, 1991/2005; Schalkwijk-Barendsen, 1991; Lincoff, 1992; Sims, Watling & Jeffries, 1995; Barron, 1999; Roody, 2003; McNeil, 2006; Miller & Miller, 2006; Boccardo et al., 2008; Buczacki et al., 2012; Guzmán et al., 2013; Kuo & Methven, 2014; Baroni, 2017; Gminder & Böhning, 2017; Kibby, 2017; Elliott & Stephenson, 2018; Jeppson, 2018; Læssøe & Petersen, 2019; Sturgeon, 2019; McKnight et al., 2021; MacKinnon & Luther, 2021.) Herb. Kuo 09029503, 08180606, 07201401, 08091917, 08112005, 09222401.

This site contains no information about the edibility or toxicity of mushrooms.

KOH

Spores

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Cite this page as:

Kuo, M. (2025, June). Scleroderma citrinum. Retrieved from the MushroomExpert.Com Web site: /scleroderma_citrinum.html