Synonym: Geastrum limbatum Fries
Fruiting body subglobose, 1.5-3.0 cm broad, hypogeous, then erumpent; exoperidium non-hygroscopic, splitting into 6-10 often unequal rays with acute tips; expanded sporocarp 5.0-9.0 cm, the tips usually lying flat, gradually becoming elevated below the spore sac; alternatively in dry weather the developing rays may become incurved and fixed permanently around the spore sac (see comments); mycelial layer encrusted with debris; pseudoparenchymatous or fleshy layer up to 4.0 mm thick, buff, pale-tan, light-grey to medium-grey, frequently areolate, sloughing away to reveal a fibrous layer, streaked or mottled ochre to dark-brown over a tan background; in senescent material, rays weathering nearly white, sometimes conspicuously ribbed, and tinged greenish from algae; spore sac 1.8-2.5 cm broad, subglobose to compressed, with or without a short pedicel and apophysis; surface of spore sac initially dusted with minute granules, soon glabrous, grey to greyish-brown; peristome slightly elevated, with an inconspicuous lighter border, the opening round to slit-shaped, fringed with stiff dark-brown hairs; gleba dark-brown.
Spores 4.5-5.5 µm excluding ornamentation, nearly round, coarsely warted; spores dark brown.
Scattered to gregarious under conifers; fairly common under Monterey cypress (Cupressus macrocarpa); fruiting from after the fall rains to late winter, occasionally during the summer months in coastal locations from fog drip.
Geastrum coronatum is a part of a group of earthstars commonly found under cypress species, especially Monterey cypress (Cupressus macrocarpa). These include Geastrum fornicatum, Geastrum saccatum, and probably several additional species. Geastrum fornicatum and G. saccatum are relatively easy to recognize, the former by a basal mycelial cup from which rays and a spore sac are elevated, the latter by recurved rays at maturity. By comparison, the characters that define Geastrum coronatum are subtle, thus it is important to see a range of material. Fieldmarks include a debris-encrusted mycelial layer, which never forms a cup, and rays which moderately elevate the spore sac. The spore sac in many specimens has a short pedicel and an apophysis, i.e. a pinched area at the base. Sporocarps that develop in dry weather, may have incurved rather than flat to slightly recurved rays and resemble hygroscopic species like Astraeus hygrometricus. Significantly, however, once the rays of Geastrum coronatum mature, they do not respond to changes in humidity.