What You Should Know
Geastrum fornicatum is an inedible species of mushroom in the family Geastraceae.
This mushroom differs from most earthstars in that the rays, rather than lying flat, "stand on their tips," elevating the spore sac. The recurved rays of Geastrum fornicatum are fixed at maturity and should not be confused with the hygroscopic rays seen in Astraeus hygrometricus and A. pteridis which fold and unfold over the spore sac with changes in humidity.
The immature fruit body is roughly spherical in shape and dark brown. At maturity, the exoperidium (outer layer) splits into four to five rays which curve backwards to elevate the fruit body and raise the spore sac for optimal spore dispersal; the tips of the rays remain attached to a basal cup. The spore sac contains an ostiole, a small opening near the apex. The mature fruiting body may be up to 6 cm (2.4 in) in diameter and 8 cm (3.1 in) tall. The exoperidium is attached to the soil by rhizomorphs.
Other names: Acrobatic Earthstar, Arched Earthstar.
Geastrum fornicatum Mushroom Identification
Fruiting body round to globose, 1.5-2.5 cm broad, the outer layer typically with embedded dirt and debris; at maturity splitting into 4-6 rays which recurve and elevate the spore sac, the tips remaining attached to a basal cup; expanded fruiting body up to 6 cm broad, and 8 cm tall; rays dark-brown, the surface scaling irregularly in age to expose a light brown under layer; spore sac 1.5-2.5 cm in diameter, rounded to slightly flattened, on a short stalk, dark brown, with a roughened surface, opening via an apical tear or slit.
Spores 3.5-4.5 µm, round, warted; dark-brown in mass.
Solitary to gregarious under conifers. In our area commonly associated with Cupressus macrocarpa (Monterey cypress); fruiting from late summer in areas of fog drip to mid-winter.
Several other Geastrum species are of the same general form, and confident identification requires a lot of expertise.
Geastrum fornicatum Antimicrobial Activity
Methanol extracts of G. fornicatum were shown to be inhibitory to the growth of various bacteria that are pathogenic to humans, including Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhimurium, and Streptococcus pyogenes, as well as the fungi Candida albicans, Rhodotorula rubra, and Kluyveromyces fragilis.
Geastrum fornicatum Taxonomy and Etymology
Descriptions of the Dwarf Earthstar date back at least as far as the late 17th century. When James Sowerby reported this fact in his treatise Colored Figures of English Fungi or Mushrooms (published in 1799) he noted that this '...strange vegetable has surprised many; and in the year 1695 it was published under the name of Fungus Anthropomorphus, and figured with human faces on the head.'
The basionym of this species dates from 1762 when the Arched Earthstar was described scientifically by British naturalist William Hudson (1730 - 1793), who gave it the binomial scientific name Lycoperdon fornicatum.
In 1821 another British botanist-mycologist, Sir William Jackson Hooker (1785 - 1865), transferred this species to the genus Geastrum and so its scientific name became Geastrum fornicatum. Hooker, incidentally, was the first Director of the Royal Botanic Gardens, Kew, an institution whose contribution to mycological knowledge has been and continues to be immense.
Synonyms of Geastrum fornicatum include Lycoperdon fornicatum Huds.
Geastrum, the generic name, comes from Geo- meaning earth, and -astrum meaning a star. Earthstar it is, then. The specific epithet fornicatum means arched.
Photo 1 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)
Photo 2 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)
Photo 3 - Author: Liz Popich (Lizzie) (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 4 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)
Photo 5 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)