Astraeus hygrometricus group represents a hygroscopic earthstar that closes in dry weather but opens in wet weather so that the star-like pointed rays of the outer layer curl out and underneath the spore case. Features include 6-15 rays, papery whitish to grayish or brownish spore case that ruptures through a poorly defined apical pore or slit, a spore mass that is white at first, brown to cocoa brown when mature, sometimes black rhizomorphs, and round finely warted spores. Phosri(1) recognized that several species have been known under this name and as a result of molecular study described 3 new species, Astraeus morganii (similar to Astraeus pteridis), Astraeus telleriae (from Europe), and Astraeus smithii Watling, M.P. Martin & Phosri. Astraeus smithii was confirmed by molecular methods from Michigan and Wisconsin and could be the correct name for the Pacific Northwest species usually called Astraeus hygrometricus [our conclusion]. The distribution is given as central and northern United States. Phosri(1) say it is "characterised by the inner peridium at maturity becoming matted-fibrillose to reticulate, the dark almost blackish rhizoids, and its unique ITS nrDNA". The description is included below.
spores 7-11 x 7-11 microns, round, finely warted , (Arora), capillitium very thick-walled, aseptate, branched, smooth or encrusted, (McKnight), spores 7.5-12.5 microns, round with a colorless sheath "overlying thickened warty layer composed of pegs"; capillitium "buff to pale brown, encrusted, thick-walled, highly branched hyphal elements", (Phosri(1) for A. smithii)
Astraeus 'hygrometricus' sensu auct. mult. found at least in BC (in Redhead(5)), OR (Zeller(2)), AZ, CA, and worldwide in distribution, (Arora), known throughout the United States, and previously reported from AZ, CA, CO, CT, FL, GA, IL, MD, MA, MI, MN, NM, NY, PA, SC, TN, TX, WA, Australia, Canada, Europe, India, Mexico and United Kingdom, (Bates), Oregon State University has collections from OR, AZ, CA, MD, OH, Japan. The Pacific Forestry Centre has collections from BC, and the University of British Columbia has collections from FL, MI, NM, and Japan. Not all of these records would correspond to the Pacific Northwest species.