Geastrum saccatum
Description
Geastrum saccatum is distinguished from the several species of earthstars that occur in the S.F. Bay area by its sessile spore sac which has a small depressed disc surrounding the apical pore and recurved non-hygroscopic rays. Young mushrooms are brown, spherical, and attached to the ground at a single point. It is inedible.
Earthstars are not particularly abundant in forested areas of the PNW. Many species are more characteristic of drier woodlands and even deserts, so the diversity of earthstars and many other gasteromycetes is much higher in the southwestern U.S. G. saccatum is widely distributed in the Northern Hemisphere and we have seen it, or a dead-ringer for it, in Tasmania, Australia.
Common names: Bowl Earthstar, Rounded Earthstar, Sessile Earthstar, Nested Earthstar.
Mushroom Identification
Ecology
Saprobic; growing alone or gregariously under hardwoods or conifers; often appearing around stumps; spring through fall (overwinter in warmer climates); widely distributed in North America.
Fruiting Body
At first a smooth, egg-shaped ball with a pointed beak, 2-3 cm wide, attached to the substrate by a point at the base; with maturity the outer skin peeling back to form 4-9 more or less triangular, buff-colored, non-hygroscopic arms; spore case up to 2 cm wide, more or less round, smooth, brownish to purplish brown, with a small conical beak that is surrounded by circular ridge or depression (often resulting in a pale area); 2-5 cm across when arms are opened; interior of spore case initially solid and white but soon powdery and medium brown.
Microscopic Features
Spores 3.5-4.5 µ; round; spiny; brownish to yellowish in KOH. Capillitial threads 4-8 µ wide; yellowish to brownish in KOH; slightly incrusted.
Look-Alikes
Is similar but the spore sac sits in a shallow cup formed from the splitting of peridial wall tissue.
has a spore sac with a short stalk and stands erect from the substrate on the tips of its rays.
Is a similar mushroom; its beak is not surrounded by a marked ridge or depression, and its buttons are attached to the substrate over a large portion of the mushroom rather than at a basal point (thus the buttons and, later, the undersides of the arms are usually covered with debris).
Geastrum saccatum Mechanism of Dehiscence
A study has shown that the formation of calcium oxalate crystals on the hyphae that form the endoperidial layer of the basidiocarp is responsible for the characteristic opening (dehiscence) of the outer peridial layers. Calcium oxalate is a common compound found in many fungi, including the earthstars. Curtis Gates Lloyd was the first to note the presence of these crystals on the endoperidium of Geaster calceus (now known as Geastrum minimum). The formation of calcium oxalate crystals stretches the layers of the outer walls, pushing the inner and outer layers of the peridium apart.
Geastrum saccatum Bioactive Compounds
A β-glucan–protein complex extracted from Geastrum saccatum was isolated and analyzed and shown to have anti-inflammatory, antioxidant, and cytotoxic activities. It is suggested that the mechanism for the anti-inflammatory activity is due to the inhibition of the enzymes nitric oxide synthase and cyclooxygenase.
Photo sources:
Photo 1 - Author: Mike Young (CC BY-SA 2.5)
Photo 2 - Author: JJ Harrison (https://www.jjharrison.com.au/) (CC BY-SA 3.0)
Photo 3 - Author: Giselle Blythe (Public Domain)
Photo 4 - Author: Cody D. Crossley (CC BY-SA 4.0)
Photo 5 - Author: Fluff Berger (CC BY-SA 4.0)
Color:Brown
Shape: Earthstars
