AT A GLANCE
- Common Name: Weathered Earthstar
- Scientific Name: Geastrum corollinum
- Category: Fungi
- Subcategory: Earthstars & Puffballs
- Range: Temperate and Mediterranean Europe, North America, and parts of Asia, occurring locally in warm, dry continental and coastal microclimates
- Habitat Type: Warm, sunny, dry, calcareous sandy grasslands, coastal sand dunes, Robinia and pine groves, parklands, and limestone steppes with thin humus
- IUCN Red List Status: Least Concern
- Lifespan: Fruiting body persists for months to years (hygroscopic rays open and close repeatedly)
- Diet: Saprobic (terrestrial decomposer breaking down dry plant litter, needles, and sandy organic humus)
- Average Size/Weight: Expanded star diameter 3 to 6 cm; central spore sac diameter 1 to 2 cm; height 1.5 to 3 cm
- Key Defining Feature: Remarkable hygroscopic earthstar with 6 to 10 pointed leathery rays that open into a star when moist and curl tightly back around the central spore sac when dry
Overview
The Weathered Earthstar (Geastrum corollinum), also known as the Corollate Earthstar, is an extraordinary, star-shaped gasteroid fungus belonging to the earthstar family Geastraceae. Looking like a miniature, leathery starfish cast upon the soil, this remarkable fungus is famous for its dynamic hygroscopic behavior: in wet, rainy weather, its pointed rays absorb moisture and peel backward to form an open star that elevates its central puffball spore sac; as the air dries, the rays curl tightly back up around the ball to protect its spores from desiccation.
Biology and Physical Characteristics
Geastrum corollinum begins its development underground as an unpretentious, subglobose, bulb-like button encrusted with sand grains. Upon maturity, the thick, three-layered outer wall (exoperidium) splits radially from the apex into 6 to 10 distinct, tapering, pointed rays that curl downward to form a star-like platform. This hygroscopic movement physically lifts the inner, papery spore sac (endoperidium) off the damp ground. The spore sac is sessile (stalkless), smooth, pale grey-brown to tan, and features an apical opening (peristome) that is conical, sharply defined, and surrounded by a circular pale halo (disc). Inside lies the gleba, which matures into a powdery brown mass of spiny basidiospores and capillitium threads.
Behavior and Ecology
The Weathered Earthstar is an ingenious biological mechanism for spore dispersal driven by rain and humidity. When raindrops strike the flexible, papery walls of the elevated central spore sac, the bellows-like puffball compresses, shooting miniature puffs of microscopic brown spores out through the central chimney into passing gusts of wind. During prolonged droughts, the rays dry out, lose turgor pressure, and curl back up over the spore sac like protective clenched fingers. The entire dried star can detach from the ground and roll across sandy dunes in the wind like a miniature tumbleweed, scattering spores as it bounces.
Conservation and Human Impact
The Weathered Earthstar is assessed as Least Concern globally, but is considered rare, localized, and red-listed as Vulnerable in several northern European countries where warm, undisturbed sandy grasslands and coastal dunes are threatened by urban development, sand mining, and vegetation encroachment.
Interesting Factoid
The Weathered Earthstar is a living botanical barometer: when rain is coming, its leathery arms automatically open up into a star, and when the air turns dry, its arms curl back up into a tight ball like clenched fingers to protect its spores.