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Species Information
Summary: {See also Earthstars Table.} 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. A. Ceska says that he once heard a radio interview with a Czech amateur mycologist reporting the blue color of Astraeus hygrometricus lasting for about three hours after opening of the fruiting body.
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.
Outer Surface: 1-5(8)cm across when fully expanded, round to flattened when young, the outer wall splitting when mature into 6-15 pointed rays, the rays "hygroscopic (unfolding in wet weather and closing up over the spore case in dry weather), often unequal in length, tough and leathery when moist, hard when dry"; underside (exterior) fibrillose, usually with adhering sand and sometimes with black hair-like threads (rhizomorphs) at base; upper surface (interior of rays) at first smooth, but often developing numerous cracks; pale tan darkening to brown, gray, or blackish brown, (Arora), 7-15 rays 2.5-5cm long, (Phillips), 1.0-2.0(3.0)cm, almost spherical or slightly ellipsoid, splitting into 7-15 rays; outer peridium "distinctly layered, surface matted-fibrillose and intermixed or embedded with sand particles, overlying a thin, fugacious layer, which breaks up, although hard when dry, seated on a fibrous-rimose innermost and exposed layer"; "with dark almost blackish rhizoids some of which persist at the base", (Phosri(1) for A. smithii)
Inner layer: spore case 0.5-3cm across, round or somewhat flattened, thin, papery; whitish to grayish or brownish; roughened by particles (and / or finely reticulate [netted]); rupturing when mature through an irregular or poorly defined apical pore or slit , (Arora), felty (Phillips), felted or netted with fibrous lines, (McKnight), "pale colored, papery-thin, the surface at maturity matted-fibrillose to reticulate, opening by a single tear", (Phosri(1) for A. smithii)
Spore Mass: brown to cocoa brown and powdery when mature, (Arora), pure white becoming brown when old, (Phillips), white when young, becoming cocoa-color when mature, (Phosri(1) for A. smithii)
Odor: negligible (Lincoff(1))
Taste: negligible (Lincoff(1))
Microscopic: 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)
Habitat / Range
single, scattered, or gregarious "in old fields, sand or sandy soil, pastures, roadsides, waste places, etc.", (Arora), almost any habitat from sandy dunes to high mountains, September to November, but sometimes keeps it shape and condition for a year or more, (Phillips), on "soil surface margins of woodland, open areas" (Phosri(1) for A. smithii)
Similar Species
{See also Earthstars Table.} Astraeus pteridis is larger, ruptures irregularly, and has "thick rays that are frequently checkered like a crooked crossword puzzle", (Arora). A. pteridis is 10-15cm across when open, with the outer surface of the rays having brown fibrils, whereas A. hygrometricus is 1-4cm across when open, often with black rhizomorphs at the base, (Ramsey). Several hygroscopic Geastrum species have a prominently grooved apical pore or spores less than 7.5 microns in diameter, (Arora). Geastrum floriforme is hygroscopic but has a small (up to 1.5cm across) smoother spore case and smaller spores, (Arora). Geastrum recolligens is hygroscopic but is smaller with smaller spores.
