Scleroderma polyrhizum
Scleroderma polyrhizum, commonly known as the star earthball or dead man's hand, is a basidiomycete fungus and a member of the genus Scleroderma, or "earthballs". Found in dry, sandy soils, this species begins completely buried before slowly forcing the soil aside as it cracks apart to form a rough, star-shaped body with a diameter of . At the center is the dark, brownish spore mass. Widely distributed wherever the soil and climate are favorable, it is known from Asia, Europe, and the Americas. Taxonomy The species was first described by Johann Friedrich Gmelin in 1792 as Lycoperdon polyrhizum. Christiaan Hendrik Persoon transferred the species to the genus Scleroderma in his 1801 work Synopsis methodica fungorum. Elias Fries's Scleroderma geaster (published in 1829) is a synonym; the epithet geaster refers to the similarity with earthstar fungi of the genus Geastrum. In 1848, Joseph-Henri Léveillé considered the star-shaped opening of mature fruit bodies to be a distinct characteristic and proposed the genus Sclerangium to contain the taxon. According to the classification of Scleroderma proposed by Gastón Guzmán in 1970, Scleroderma polyrhizum is placed in the subgenus Sclerangium, which includes species with partially reticulate spores. Common names that have been used for the fungus include: many-rooted earthball, earthstar scleroderma, star earthball, and dead man's hand. Description When unopened, the fruit body ranges in shape from round to flattened to somewhat irregular, sometimes with lobes. As the mushroom matures, the peridium (outer skin) opens in a star-like manner to form 4–8 rays that curl back and expose the inner spore mass (gleba). Typically, more than half of the fruit bodies remains buried in the ground, attached by white, string-like or flattened strands rhizomorphs. The peridium is tough and thick, typically , with a rough and cracked surface. It is initially white, then turns yellowish to light brown as it matures. When unopened, the fruit body is wide, expanding to after rupturing. In young specimens, the gleba is firm and light grey, but it becomes dark brown and powdery after the spores mature. The spores are spherical, partially reticulate with warts or spines, and measure 6–11 μm. A drop of dilute potassium hydroxide placed on the surface of the fruit body will either be nonreactive or turn the peridium slightly yellow. The species contains toxins which, if ingested, cause serious gastric upset. It is also similar to other poisonous species. Similar species Scleroderma texense has a fruitbody similar in appearance to S. polyrhizum. Some authors have considered them synonymous, but Guzmán's 1970 study of the type showed that S. texense is distinct. It typically has an exoperidium that is more yellowish or orangish, with thick, folded scales in maturity. S. citrinum is also similar. Habitat and distribution Fruit bodies of Scleroderma polyrhizum grow singly, scattered, or in clusters, usually on hard clay or sandy soil, gravel, in lawns, or bare soil. Fruiting occurs in late summer and fall, although blackened rays can sometimes be found in the winter. It has a wide distribution in North