Earthstars - the Latin name is Astraeus hygrometricus) are fungi, a close relation to puffballs. Most people have seen puffballs - irregularly shaped ball-like mushrooms that are just dry spore sacks that make a satisfying "pop" when stepped on.
Earthstars have an outside covering to their puffball that opens and reveals the puffball as it grows. The outer covering splits into a leathery star around the 50-cent sized whitish puffball.
Amateur naturalists have often found hundreds of Earthstars growing in the Shin Oak sand dunes east of the Pecos River and other patches of sandy soil in West Texas and eastern New Mexico. A few have also been found in home landscapes, and even practice football fields. The evidence points to a mycorrhizal (my-co-rye-z al)relationship with the Shin Oaks (Quercus havardii) in that habitat, but in other habitats, their mycorrhizal partners may be another species of oak and possibly other species of woody plants.
The Earthstar mycelium (the vegetative form of the fungus) forms a sheath of fungus around the tiniest rootlets of trees and shrubs. The fungus cells penetrate the cells of the rootlet. Through the fungus, the tree or shrub obtains nitrogen, phosphorus and other nutrients present in the soil. The fungus survives in the vegetative state for years.
After good soaking rains the plant finally spores, "blooming" with microscopic seed-like germ plasm (or spores) that can float on the air rising from the soil. If humans or animals don’t step on and pop the Earthstar, it eventually has an "ostiole" form - a vent in the top of the ballooned out puffball. As the winds whirl and blow, the spores are wafted out by the hundreds of thousands - dust-like particles floating everywhere.
Nathan Taylor, a young naturalist near Lamesa, who lives in Shin Oak habitat has closely watched the earth stars on his property, and has noticed the spores are released early in the morning, when the relative humidity is the highest. The spores sometimes emerge thickly enough to be seen with the unaided eye. Like juniper pollen, the spores float at what seems to be the top of a layer of humid air, right where drier air meets it. Wind quickly disperses the spores as the day heats up and dries out.
Young specimens resemble a puffball unopened. The earthstar shape is a result of the outer layer of fruiting body tissue splitting open in a star-like manner. The earthstar grows in association with various trees, especially in sandy soils. It’s found worldwide in both temperate and tropical regions. The species name refers to the fact that it‘s water-absorbing and can open up its rays to expose the spore sac in response to increased humidity and close them up again in drier conditions. The rays have an irregularly cracked surface, while the spore case is pale brown and smooth with an irregular slit or tear at the top.
Sometimes the closed up earthstars detach from the ground, and our strong hot winds will cause them to roll, and thereby release stores through the cracks between the rays of the fruiting body.
Earthstars are considered inedible in North America, but in Asia they sometimes appear in markets to be sautéed in oil. The spore dust has been used in herbal medicine in Asia as a means to slow bleeding. Ethanol extracts of the fruit body are high in antioxidant activity, and have been shown in laboratory tests to be anti-inflammatory and comparable to modern drugs.
If someone claims to have seen stars on the ground, they’re not crazy!
Nature Notes is sponsored by the Dixon Water Foundation and is produced by KRTS Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Burr Williams of the Sibley Nature Center.
