The Geastrales are an order of gasterocarpic basidiomycetes (fungi) that are related to the Gomphales. The order contains the families Geastraceae—which include the "earthstars" formerly placed in Lycoperdales or Phallales,
In Geastrum, once mature, the exoperidium splits into a variable number of rays, which give them their visible star shape. The exoperidial rays are there to protect the endoperidial body and orchestrate spore dispersal. The fruiting bodies of several earthstars are hygrometric: in dry weather the rays will dry and curl up around the soft spore sac, protecting it. In this state, often the whole fungus becomes detached from the ground and may roll around like a tumbleweed. In wetter weather, the rays moisten and uncurl; some even curl backward lifting the spore sac up. This allows rain or animals to hit the spore sac, emitting spores when enough moisture is present for them to germinate and establish.