Geastrum minimum or tiny earthstar 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.^[3] It is a priority species in the UK, where it has been found in the sand dunes at Holkham National Nature Reserve.^[4][5]

The species was first described by Lewis David de Schweinitz in 1822.^[2]

Fruit bodies are initially roughly spherical before the outer peridium splits to form a star with 6–11 "rays". When opened, the diameter of the fruit body is 1–3 centimetres (1⁄2–1+1⁄4 in). The inner spore sac is spherical or egg-shaped, and measures 0.5–1 cm (1⁄4–1⁄2 in). The more-or-less round spores measure 5–5.5–4–4.5 μm and have warts on their surface.^[6]