Anamorph: not known.
Teleomorph: basidioma 1.5-3 cm diam. when expanded; endoperidium 6–12(-16) mm diam., pale grey-brown and covered in whitish-grey crystalline pruina when fresh, subglobose; peristome fimbriate/fibrillose, delimited with a weak groove; columella whitish, cylindric/clavate, may be poorly defined; mature gleba brown; pseudoparenchymatous layer pale when young, growing darker and splitting with age, may form a collar around the stalk; stalk brown, 1 mm tall; 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. Basidiospores 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. Fruiting bodies often found in groups.
Assessed as Vulnerable / D1 in Great Britain by Ainsworth (currently in review by JNCC/NE). UK records were formerly reported as Geastrum minimum. That taxon was classed as Vulnerable / D2 in GB&IoM in the provisional Red Data List of Threatened British Fungi (Evans et al., 2006), and is listed as a UK BAP priority species. G. minimum sensu stricto appears not to occur in our region.
Members of the G. minimum agg. include a number of morphologically similar species, detailed in Zamora et al. (2015).
Geastrum schmidelii is similar in size and macroscopic appearance, and found in similar habitats. It differs in possessing a sulcate peristome (outside of the “mouth” slit clearly marked with parallel grooves) while that of G. marginatum is fibrillose (covered in minute hairs).
G. coronatum has robust and much larger fruitbodies (3-10 cm when expanded), with a fibrillose peristome, dark stalk and glabrous endoperidial surface, covered with a ‘mealy’ mesoperidium formed by abundant but rather indistinct hyphae. Basidiospores are also very distinct from G. minimum.
G. quadrifidum should be clearly distinguishable in possessing a fornicate exoperidium, with (3-)4-5(-6) rays, the margins of rays conspicuously rolled out. A very similar species, G. britannicum, has also been recently described in the UK, differing in basidiospore and peristome micromorphology (Zamora et al., 2015). G. quadrifidum is currently considered Vulnerable (Evans et al. 2006), while G. britannicum is now known from about 15 sites.
Often found on mosses, with Pinus nigra, grasses and sedges.
In GB&I, specimens are reported from VC28 W Norfolk, VC69 Westmorland and VC70 Cumberland.
Coastal dune habitat. This species is reported on or near dunes or dune slack, in sandy soils, sometimes near pine.