About Geastrum michelianum Berk. & Broome
Like all fungi, the visible fruit body of Geastrum triplex is part of a larger hidden organism. The hidden, nearly invisible fungal thread masses that form the fungus's active feeding and growing structures are called mycelium. Fruit bodies form when environmental conditions such as temperature, moisture, and nutrient availability are optimal, and their function is to produce and disseminate spores. Geastrum triplex has the largest fruit bodies among all earthstar mushrooms. Immature fruit bodies are typically 1 to 5 cm (1โ2 to 2 in) in diameter; when their rays are fully spread, they are usually up to 8 to 10 cm (3+1โ4 to 4 in) broad, and may reach an exceptional maximum size of 11.5 cm. The fruit body contains a roughly spherical to egg-shaped inner structure called the endoperidium, which is topped by an opening called the ostiole. Tissue fragments around the ostiole form a small pointed beak known as the peristome. The endoperidium is typically sessile (it lacks any sort of stem). When young, it is grayish brown to wood brown; dried unopened specimens are light yellow-brown. The outer tissue layer is called the exoperidium; it develops splits that radiate from the apex, forming between four and eight rays that separate away from the endoperidium. The thin papery endoperidium surrounds a mass of spores and fertile tissue known as the gleba. The central part of the gleba contains a pseudocolumella, a columella not attached to any stalk. The pseudocolumella is typically cylindrical or club-shaped, and extends upward from the base. It has limited value for identification due to variability in its persistence, size, structure, and shape across the genus. The rays of the exoperidium are 2 to 4 cm (3โ4 to 1+1โ2 in) long, and up to 4 mm (3โ16 in) thick. After expansion, the lower (outer) surface of the rays and the surface of unopened specimens have a rough texture. Unlike many other Geastrum species, dirt and debris do not adhere to the underside of G. triplex rays. When dried, the inner fleshy upper surface of these rays is near wood brown in color, and its surface tissue layer cracks into patches. There is substantial variation in how much the upper surface tissue cracks: the layer may remain closely attached as a sheet over the unsegmented part of the outer wall, while the portion attached to the rays cracks to varying degrees, and sometimes peels away completely in places. In G. triplex, the base of the rays usually breaks around the perimeter of the endoperidium, forming a saucer-shaped platform or receptacle that the endoperidium rests on. Not all specimens develop this receptacle, which can lead to confusion with other Geastrum species. Curtis Gates Lloyd reported that in tropical regions with abundant high temperatures and humidity, the fungus expands rapidly, making it more likely for the fleshy layer to break away and form a receptacle. In more temperate areas, this effect is less pronounced, and usually does not occur at all. The endoperidium is 1 to 3 cm (3โ8 to 1+1โ8 in) in diameter, 0.9 to 2 cm (3โ8 to 3โ4 in) high, sessile, and dull grayish brown. The peristome is made of radially arranged fibrils that clump together at the apex in groups of unequal length, creating an opening that looks jagged or torn. The circular area bordering the peristome is paler in color. Microscopically, the gleba inside the spore sac contains the pseudocolumella, unbranched threads called capillitium, spore-bearing cells called basidia, and spores. All these microscopic elements have characteristic features that help distinguish G. triplex from other superficially similar earthstars. Spores are dispersed either when wind blows over the ostiole and pulls spores out, or when falling raindrops hit the flexible endoperidium, creating a puff of air that forces spores out through the opening. The spores are spherical, 3.5โ4.5 ฮผm in diameter. They are covered with short, narrow projections that end abruptly, made of translucent hyaline substance. The spores turn pale cinnamon brown in potassium hydroxide, and dark dull brown (nearly sepia) when stained with iodine. The capillitium is made of apparently encrusted cylindrical filaments 3โ6 ฮผm in diameter. Their color ranges from hyaline to dull yellowish brown in potassium hydroxide, and yellowish in iodine. Their walls are thickened enough that the internal lumen appears only as a thin line. Basidia have either two or four spores attached, and the sterigmata (basidia extensions that hold the spores) are long, up to 20 ฮผm. Geastrum triplex does not produce cystidia. Geastrum triplex is a saprobic fungus, meaning it gets nutrients from decomposing organic matter. Its fruit bodies usually grow singly, or more commonly in groups, in hardwood forests with accumulated humus; in Mexico, specimens have been collected in tropical deciduous forest. Fruit bodies are often found around well-rotted tree stumps. They start out almost buried in loose duff, but emerge as they mature, when downward curling of the rays exposes the spore sac. Old fruit bodies are persistent, and may survive the winter to be found the following spring or summer. A Dutch study noted that G. triplex tends to grow on calcium-rich soil formed from washed-out chalk of crushed shells along bicycling paths. It is described as common in North America and Europe, and one author notes it is commonly found growing under beech trees. G. triplex has a widespread distribution, and has been collected in Asia (China, Korea, Iran, and Turkey), Australia, Europe (Belgium, Czech Republic, Sweden, and the Canary Islands), and Africa (Congo, South Africa). In North America, its range extends north to Canada, south to Mexico, and covers all of the continental United States as well as Hawaii. In Central and South America, the fungus has been reported from Panama, Trinidad and Tobago, Argentina, Brazil, and Chile. Earthstars were used medicinally by indigenous peoples of the Americas. The Blackfoot called this species ka-ka-toos, meaning "fallen stars", and legend holds it indicates supernatural events. The Cherokee placed fruit bodies on babies' navels after childbirth, until the withered umbilical cord fell off, using it both as a prophylactic and a therapeutic measure. In traditional Chinese medicine, G. triplex is used to reduce inflammation in the respiratory tract, stanch bleeding, and reduce swelling.
