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Barometer Earthstar
Astraeus hygrometricus

From MLBS: The Barometer Earthstar is so named because of its peculiar ability to read the air humidity. The different parts of the rays absorb water at different rates, giving the earthstar this unusual power. At times when the air or the ground below it is moist, the rays unfold to their fullest extent, raising the earthstar high above the ground. When a raindrop strikes the spore sac, spores are released in a burst, and their newly gained elevation increases the chance of them being caught by the wind and scattered far and wide. However, when the ground and the air are dry, the rays will lower the spore sac back to the ground and curl up around it, probably to protect it from predators or the elements. An earthstar may take only five minutes to completely open up, an almost visible process. However, it can take days to close again, likely because of the moisture remaining in the rays. Earthstars can remain in states like that for several years, even separate from the mycelium. However, when all the spores have been distributed, the earthstar disintegrates, leaving the rays opens.

Habitat: Sand or sandy soil, under hardwoods and conifers. Fruiting in summer and fall.

This fungus is mycorrhizal with many different plants. (A mycorrhiza is a symbiotic association between a green plant and a fungus. The plant makes organic molecules such as sugars by photosynthesis and supplies them to the fungus, and the fungus supplies to the plant water and mineral nutrients, such as phosphorus, taken from the soil.)

This earthstar is also known as a “False Earthstar” because in the 1800s it was re-classified into a different family Astraeaceae, rather than the family of true earthstars, Geastrum.

Again, from MLBS: “The young fruiting body of a Barometer Earthstar is a round sac partially embedded in the soil. As it matures, the exoperidium (outer skin) breaks open into numerous rays in a star-shaped pattern.  As they split apart, they reveal the spherical spore sac, enclosed in the endoperidium (inner skin). The rays unfold, pushing the spore sac into the air where the spores can be spread. Sometimes, they push it up hard enough to break its connection to the mycelium.”

All text and photos copyright © 2022 Middle Way Nature Reserve, unless noted.
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