Astraeus hygrometricus is an ectomycorrhizal fungus that grows in association with roots of different plant species. During the maturation phases the mycelial layer tears away, and the outer tissue layer breaks open forming a star shape. At the same time, thanks to the different layers of tissue that make up exoperidium the fruit's body appear above the ground to reveal a round spore case. Specifically, the innermost fibrous layer is hygroscopic, and is able to wrinkle or stretch the entire ray in response to moisture conditions. In this way the rays respond to environmental moisture conditions, opening up at high humidity to release the spores, and closing when the air is dry.