Cleland & Cheel (1915) 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 – 1 to 2.5 cm (1⁄2 to 1 in) broad – spore sac.

Although uncommon, G. 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.

[3] In 1860, Miles Joseph Berkeley and Moses Ashley Curtis described the species Geastrum biplicatum (originally named Geaster biplicatus),[4] based on specimens sent to them by Charles Wright that he obtained from the Bonin Islands during the North Pacific Exploring and Surveying Expedition.

[10] Samuel Frederick Gray called it the "comblike shell-puff" in his 1821 "A Natural Arrangement of British Plants".

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).

Internally, the endoperidium contains a structure called the columella that is narrowly conical in shape, whitish or pale brown, and extends more than halfway into the gleba.

The latter species lacks vertical striations on the basal portions of the endoperidium, and does not have a pseudoparenchymatous collar around the stem.

[24] G. xerophilum also has a dusting of white powder on the surface of the spore sac, but unlike G. pectinatum, consistently lacks a ring at the base of the pedicel; furthermore, in contrast to G. pectinatum, the spores of G. xerophilum are yellow and contain oil drops that are readily observable with a microscope.

[24] The species has been noted to occur in late summer and autumn (in Britain and Europe),[18] but the fruit bodies may dry and persist for some time.

[44] North American sources gives its frequency of appearance as "rare",[10][12] but Stellan Sunhede, in his 1989 monograph on the Geastraceae, considers it one of the most common earthstar mushrooms of northern Europe.

[47] The presence of calcium oxalate crystals—apparent as a whitish powder on the surface of the spore sac—has been verified for G. pectinatum using scanning electron microscopy.

[48] A study on the related species Geastrum saccatum has shown that these crystals are responsible for the characteristic opening (dehiscence) of the outer peridial layers.