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Nature Notebook – False Earthstar Fungus

About a month ago, our staff happened upon an interesting star-shaped fungus during an exploratory hike on a newly acquired property. “It’s an earthstar fungus!” said a staff member. I snapped a photo and we went on our way.

Upon further investigation, I learned this mushroom isn’t in the earthstar family at all, but is called a false earthstar, or astraeus hygrometricus.

Its name comes from Greek, meaning star-shaped and measures humidity. This inedible fungus reacts to the humidity in the air, distending or retracting its outer layer depending on moisture.

On a humid day, a false earthstar will open its rays to expose its spore sac, and then close them when conditions are drier. This allows the fruit body to disperse spores at optimum moisture and reduce evaporation during dry times.

False earthstar is ground dwelling and prefers nutrient poor or sandy soils near pine or oak trees and open fields.