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Excerpts from Jim Conrad's
Naturalist Newsletter
from the December 15, 2013 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau; elevation ~1750m (~5750 ft); N29.62°, W99.86°; USA
BAROMETER EARTHSTAR
On the slope below Juniper House, where the power company has cut a swath of trees for their lines, on thin, moss-covered soil, the pretty little object turned up shown above. The spherical centerpiece, which is basically a typical puffball fungus filled with spores, is only half an inch across (15mm).
If you walk in wild places looking at the ground you've seen this kind of thing before, and probably know that it's a kind of fungus known as an earthstar. However, there are many earthstar species, so part of the fun becomes figuring out which species this is.
Most earthstars I've run into belonged to the genus Geastrum, but it turns out that this one belongs to an entirely different genus, Astraeus.
*UPDATE: In 2013 I identified this as Astraeus hygrometricus. In 2025, many more identification resources are available on the Internet. When this page's images are uploaded to iNaturalist, user "pynklynx" disagreed with that ID, with no further comment. When I look into the matter, a web page at FungiKingdom.net says this: "Astreus morganii (Phosri, Watling & P.M. Martin 2013) is called the North American ‘Barometer Earthstar’. The name Astreas hogrometricus is used now for the European version of this earthstar." So, in 2013 a new name was published, separating fungi in North America from similar- or same-looking fungi in Europe known as Astreus hybrometricu. That new name was ASTRAEUS MORGANII, which is the new name for the fungi shown on this page. In English, we still refer to the species as the Barometer Earthstar.
Species in this genus often are known as False Earthstars because they're not members of the "true earthstar genus," Geastrum. The common name Barometer Earthstar is used because when the air is moist, usually the case when the barometer is low, the "arms" surrounding the puffball open up, forming the star. But when the air is dry the arms close up. Below, you can see the same earthstar pictured above after spending a day on a saucer in my dry room:
Astraeus morganii occurs in the southwestern and parts of eastern US, into the Mexican highlands.