Monday 13th September 2021

Myriostoma is a fungal genus in the family Geastraceae. The genus is has four species, with the type species being Myriostoma coliforme.

It is an earthstar, so named because the spore-bearing sac’s outer wall splits open into the shape of a star. The inedible fungus has a cosmopolitan distribution, and has been found in Africa, Asia, North and South America, and Europe, where it grows in humus-rich forests or in woodlands, especially on well-drained and sandy soils. A somewhat rare fungus, it appears on the Red Lists of 12 European countries, and in 2004 it was one of 33 species proposed for protection under the Bern Convention by the European Council for Conservation of Fungi.

The fruit body, initially shaped like a puffball, is encased within an outer covering that splits open from the top to form rays. These rays curve down to expose an inner papery spore case, which contains the fertile spore-bearing tissue, the gleba. The fungus is unique among the earthstars in having a spore case that is supported by multiple stalks, and is perforated by several small holes suggestive of its common names salt-shaker earthstar and pepperpot. It is the largest of the earthstar fungi, and reaches diameters of up to 4.7 in. Its spherical spores have elongated warts that create a ridge-like pattern on their surface. The spores are dispersed when falling water hits the outer wall of the spore sac, creating puffs of air that force the spores through the holes.

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