Fungi are a common occurrence in most humid areas growing on trees, rocks, and on the ground where suitable conditions are present. The false earthstar or the hygroscopic earthstar is a fungus of the family Diplocystaceae. The false earthstar is a fungus of the genus Astraeus that derives its name from its star-shaped rays. The fungus consists of about 6-15 pointed rays that surround a spore sac. The surface of the pointed rays is scaled, and are formed after the fruit body, which develops when they are submerged in the substrate, matures leading to the separation of the outer layer (exoperidium). After maturity and separation of the exoperidium, the inner part of the fruit body rises above the ground to form the spore sac. The pointed rays and spores have a brownish color and produce a mushroomy smell when moist. When dry, the spore sac releases a brown dust.
The false earthstar responds to the stimulus by the moisture content of the air and the soil in which they grow. The response of the fungus to moisture has earned it the name barometer earthstar. In times of high humidity, the rays of stars of the false earthstar absorb the moisture and open to expose the spore sac. These rays contract in dry conditions closing over the spore sac to protect it from damage by predators such as snails and to reduce evaporation. The response of the rays to moisture is an adaptation that allows dispersal of spores at times of optimum moisture conditions.
The false earthstar reproduces through spores. The fungus depends on the wind as well as humidity for dispersal. When the humidity is high, the outer rays absorb the moisture exposing the spore sac, which opens and releases spores. When the air is dry, the pointed rays of the fungi close up. When very dry, the closed mass becomes light and is rolled away by wind thus dispersing the spores. In the suitable substrate, the spores develop into new fungi. Most of the fruiting occurs during the rainy season.
The false earthstar is distributed mostly in tropical and temperate regions of Africa, Asia, Australia, North and South America, and Europe where it grows on trees. In these habitats, the false earthstar coexists in a mutually beneficial symbiotic relationship with the tree roots. The fungus obtains carbohydrates from the trees while the tree roots acquire nutrients from the soil. Some of the trees with the fungus associates include Sal, oak, pine, and Chir pine. The fungus prefers loamy or sandy substrates and sometimes-on rocky areas with slate or granite substrates.
The traditional Chinese and Indians have used the fungus in medicine. The various forms of the fungi have been used on external bleeding of wounds, and as a salve for burns when the spores are blended with mustard seed oil. In Nepal and south Bengal, the false earthstar is a local delicacy also sold in markets. However, in many areas, the fungus is considered inedible due to its hard texture as well as fears of the fungi being poisonous. The dried fungi may be used as a table decoration. The false earthstar has been subject of several scientific researches to examine the bioactive compounds and its effect on the immunity.