Geastrum pectinatum is an inedible species of mushroom belonging to the earthstar family of fungi. Although young specimens are spherical, fruit body development involves the outer layer of tissue splitting open like a star into 7 to 10 pointed rays that eventually bend back to point downward, revealing a small – broad – spore sac. The spore sac is supported by a small radially wrinkled stalk. There is a distinct conical opening (peristome) at the top of the spore sac that is up to long. It is commonly known as the beaked earthstar or the beret earthstar, in reference to the shape of the spore sac and its prominent, protruding peristome. The mass of spores and surrounding cells within the sac, the gleba, is dark-brown, and becomes powdery in mature specimens. Spores are spherical, measuring 4 to 6 micrometers in diameter, with warts on their surfaces. Although uncommon, Geastrum pectinatum has a cosmopolitan distribution, and has been collected in various locations in Europe, North and South America, Asia, Australia and Africa, where it grows on the ground in open woods. Like several other earthstars, crystals of calcium oxalate are found on G. pectinatum, and are thought to be involved in fruit body maturation.
Taxonomy, classification, and naming
Christian Hendrik Persoon published the first description of Geastrum pectinatum in 1801. In 1860, Miles Joseph Berkeley and Moses Ashley Curtis described the species Geastrum biplicatum (originally named Geaster biplicatus), based on specimens sent to them by Charles Wright that he obtained from the Bonin Islands during the North Pacific Exploring and Surveying Expedition. Japanese mycologist Sanshi Imai considered this identical with G. pectinatum in a 1936 publication. In 1959, mycologist J.T. Palmer reported comparing the original specimen collected by Persoon with fresh samples of what were then thought to be the distinct species G. plicatum and G. tenuipes (named by English naturalist Miles Joseph Berkeley in 1838 and 1848, respectively) and concluded the three specimens were synonymous; the original Persoon specimen was then designated as the neotype.
In Ponce de Leon's classification of Geastrum, he placed the species in the subgenus Geastrum, section Geastrum, as the type of the subsection Sulcostomata, group Pectinatum. Other species in this group—characterized by a determinate peristome surrounded by a groove—are G. xerophilum, and G. furfuraceum. In Stanek's (1958) infrageneric concept, G. pectinatum is placed in section Perimyceliata (encompassing species whereby the mycelial layer covers the entire endoperidium), in subsection Glabrostomata, which includes species with plicate peristomes.
The specific epithet is derived from the Latin pectinatum, "like a comb". Its common names include the "beaked earthstar" or the "beret earthstar". Samuel Frederick Gray called it the "comblike shell-puff" in his 1821 "A Natural Arrangement of British Plants".
Description
Immature specimens – diameter – are roughly spherical and begin their development submerged in the ground, but gradually push above ground during maturation. In this state the outer surface is covered with mycelia, which forms a soft, fluffy coat that holds soil and debris to the outer surface. The young fruit bodies often have a rounded knob or protuberance. Like other members of genus Geastrum, G. pectinatum has a fruit body wall that is multilayered. At maturity, the outer layer (the exoperidium) splits open from the top in a stellate (star-shaped) manner into 7–9 rays that support the spore sac contained within the inner wall (the endoperidium). The expanded specimens are up to broad and tall. The rays of the exoperidium bend back (reflex), simultaneously elevating the spore sac above the ground in what is known as the fornicate condition; this position exposes the spore sac to more air currents, aiding spore dispersal. The surface of the rays often crack to reveal lighter-colored areas, especially along the edges. Together with a well-developed layer of mycelium, the rays are typically bound to fragments of earth or forest duff.