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The Collaborative International Dictionary

Geastrum \Geastrum\ prop. n. The type genus of the Geastraceae, consisting of fungi whose outer peridium when dry splits into starlike segments.

Syn: genus Geastrum.


Geastrum ( orthographical variantGeaster) is a genus of mushroom in the family Geastraceae. Many species are known commonly as earthstars.

The name comes from geo meaning earth and aster meaning star.

The name refers to the behavior of the outer peridium. At maturity, the outer layer of the fruiting body splits into segments which turn outward creating a star-like pattern on the ground. The inner peridium is a spore sack. In some species, the outer peridium splits from a middle layer, causing the spore sack to arch off the ground. If the outer peridium opens when wet and closes when dry, it is described as hygroscopic.

In some species, the inner peridium is borne on a stalk or pedicel. The columella is a column-like clump of sterile tissue to be found inside the inner peridium. The network of fertile tissue inside the inner peridium, the capillitium, arises from the columella. The mouth in most species of "earth-stars" is quite prominent, often arising as a small cone at the apex of the inner peridium. It may be even or sulcate (grooved).

They are generally not toxic but considered non-edible due to their fibrous texture in the mature stage that they are generally found at.