Immature specimens – 1 to 2 cm (0.4 to 0.8 in) 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 5 cm (2.0 in) broad and 6 cm (2.4 in) 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.

The tough and membranous endoperidium comprising the spore sac, purple-brown in color and 0.5 to 1.5 cm (0.2 to 0.6 in) tall by 1 to 2.5 cm (0.4 to 1.0 in) wide, is supported by a small stalk—a pedicel—that is 3–4 mm long by 7–10 mm wide and which has a grooved (sulcate) apophysis, or swelling.
This ring-shaped swelling is made of remnants from a tissue called the pseudoparenchymatous layer.
When fresh, the pseudoparenchymatous layer is whitish in color, thick and fleshy; it dries to become brown to dark brown while shrinking and often splitting and peeling.
The endoperidium may be pruinose—covered with fine, white, powder—although the presence of this characteristic has been noted as being somewhat variable.
The spore sac is opened by a single apical pore atop a conical "beak", or peristome.
The peristome is pectinate—made of tissue that resembles the teeth of a comb; the specific epithet is named after this characteristic.
The peristome is 2 to 5 mm (0.08 to 0.20 in) long, and comprises 20–32 distinct ridges.
The mass of spores and surrounding cells within the sac, the gleba, is dark-brown, and becomes powdery in mature specimens.
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.
G. pectinatum has no distinguishable odor or taste; like other earthstar mushrooms, it is inedible, and of "no alimentary interest".
Immature specimens – 1 to 2 cm (0.4 to 0.8 in) 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 5 cm (2.0 in) broad and 6 cm (2.4 in) 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.
The tough and membranous endoperidium comprising the spore sac, purple-brown in color and 0.5 to 1.5 cm (0.2 to 0.6 in) tall by 1 to 2.5 cm (0.4 to 1.0 in) wide, is supported by a small stalk—a pedicel—that is 3–4 mm long by 7–10 mm wide and which has a grooved (sulcate) apophysis, or swelling. This ring-shaped swelling is made of remnants from a tissue called the pseudoparenchymatous layer. When fresh, the pseudoparenchymatous layer is whitish in color, thick and fleshy; it dries to become brown to dark brown while shrinking and often splitting and peeling. The endoperidium may be pruinose—covered with fine, white, powder—although the presence of this characteristic has been noted as being somewhat variable. The spore sac is opened by a single apical pore atop a conical "beak", or peristome. The peristome is pectinate—made of tissue that resembles the teeth of a comb; the specific epithet is named after this characteristic. The peristome is 2 to 5 mm (0.08 to 0.20 in) long, and comprises 20–32 distinct ridges. The mass of spores and surrounding cells within the sac, the gleba, is dark-brown, and becomes powdery in mature specimens. 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. G. pectinatum has no distinguishable odor or taste; like other earthstar mushrooms, it is inedible, and of "no alimentary interest".
Geastrum pectinatum