Barometer Earthstars

Astraeus is a widespread genus of bolete mushrooms. It occurs in North America, Central America, Europe, Asia, Australia, and New Zealand. There are currently nine recognized Astraeus species worldwide, three species in North America north of Mexico, and just one species in Minnesota.

Astraeus species grow on the ground. They have a mutually beneficial relationship (mycorrhizal) with the tiny rootlets of trees and shrubs, absorbing sugars and amino acids while helping the tree absorb water.

Astraeus species look like earthstars in the genus Geastrum but they are not closely related. Astraeus species are in the order Boletales. They get their nutrients from the living rootlets of trees and shrubs. They are found in forests, woodlands, and open areas, always near trees or shrubs. Geastrum species are in the order Geastrales. They get their nutrients from decaying organic material (saprobic). They are found in deserts and other arid and semi-arid habitats.

The fruiting body is a thick layer of flesh surrounding a round spore sac. As it matures, the outer layer splits into rays. The rays are hygroscopic. When moist, they are open and bent backward beyond the horizontal, elevating the spore sac above the ground. When dry, they close up and surround the spore sac.

Sources

4, 24, 26, 29, 30, 77.

Family
An analysis of the genus Astraeus (Ervin, Marion D. (1951) "Astraeus and Geastrum," Proceedings of the Iowa Academy of Science, 58(1), 97-99) concluded that the genus should be in its own family Astraeaceae. It was later moved to the family Diplocystidiaceae, but the move was not universally accepted. Some sources, including Index Fungorum, MycoBank, GBIF, and ITIS, place the genus in the family Diplocystidiaceae. Other sources, including NCBI, NatureServe, and iNaturalist, place it in the family Astraeaceae.

Species
The genus Astraeus was previously thought to contain a single highly variable species, Astraeus hygrometricus, with a worldwide distribution. In 1948 Scleroderma pteridis, found in North America, was transferred to the genus as Astraeus pteridis. Some authors treated it as a subspecies of Astraeus hygrometricus.

Molecular and phylogenetic studies since 2003 have identified several new species that were previously classified as A. hygrometricus. The most recent of these studies (Phosri et al., 2013) showed that the type species, A. hygrometricus, occurs only in southern France and Turkey. In the United States, western specimens were grouped under A. pteridis. Two new species were described, A. morganii in southern U.S. and Mexico, and A. smithii in central and northern U.S.

According to Michael Kuo (MushroomExpert.com), the 2013 paper “…is riddled with errors, inconsistent species descriptions, and poor documentation; I believe further research is required before accepting the paper's suggestions.”

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Location: Uncas Dunes SNA