Geastrum minimum

Description

Geastrum minimum is an inedible species of mushroom belonging to the genus Geastrum. Although rare, it is widespread in Europe, where it occurs in a range of habitats. It is a priority species in the UK, where it has been found in the dunes at Holkham National Nature Reserve.

Fruit bodies are initially roughly spherical before the outer peridium splits to form a star with 6–11 "rays". The inner spore sac is spherical or egg-shaped. The more-or-less round spores and have warts on their surface.

The species was first described by Lewis David de Schweinitz in 1822.

Common names: Tiny Earthstar.

Mushroom Identification

1. Fruit Body

   1.5-3 cm diam. when expanded; endoperidium 6–12(-16) mm diam., pale gray-brown and covered in whitish-gray crystalline pruina when fresh, subglobose; peristome fimbriate/fibrillose, delimited with a weak groove; columella whitish, cylindric/clavate, may be poorly defined; mature gleba brown; pseudoparenchymous layer pale when young, growing darker and splitting with age, may form a collar around the stalk; stalk brown, 1 mm tall.

2. Exoperidium

   Splitting into 6-10 arching rays; not fornicate (i.e. the fruitbody is not elevated by arching rays to the extent of separation of its base from the mycelial layer below); mycelial layer persistent and encrusting debris; capillitial hyphae yellow-brown, 3-6 μm diam., thick-walled, tapering towards tips, irregularly encrusted, sometimes forked;

3. Spores

   Dark brown, globose, 5-6 μm diam. excluding ornamentation, 5.5-7.5 including; spore ornamentation irregular, composed of coarse verruculae 0.4-0.7 μm tall and 2 μm diam.

4. Habitat

   Coastal dune habitat. This species is reported on or near dunes or dune slack, in sandy soils, and sometimes near pine. Fruiting bodies are often found in groups.

Photo sources:

Photo 1 - Author: alan_rockefeller (Attribution-ShareAlike 4.0 International)

Photo 2 - Author: ma_sche (CC BY 4.0)