The cap of the fruit body is thin and membranous, measuring 3 to 20 mm (0.1 to 0.8 in) in diameter.
It has a convex shape slightly depressed in the center, conspicuous furrows in an outline of the gills, and scalloped edges.
Young, unexpanded caps are yellowish brown; as the cap expands, the color lightens to whitish or light pinkish-white, often with a darker, sometimes brown center.
The variety fusca has brown caps.
 The white or slightly yellowish flesh is very thin, reaching about 0.25–1.5 mm thick in the central part of the cap, and even thinner at the margin.

Gills are attached to a collar, never to the stem, although some specimens have the collar pressed close enough to it that this characteristic may be less obvious.
Widely spaced, they have the same whitish to pale yellow color as the flesh, and typically number between 16 and 22.
They are initially narrow, but thicken downward to about 1–3 mm at the exposed edge.
The stem is 1.2 to 8.0 cm (0.5 to 3.1 in) long and up to 0.15 cm (0.06 in) thick, with a smooth, sometimes shiny surface.
It is tough, hollow, and either straight or with some curving.
The color is blackish-brown up to a lighter, almost translucent apex.
The base of the stem may be connected to dark brown or black root-like rhizomorphs 0.1–0.3 mm thick.
Mature specimens display no veil.

Details of the fruit bodies' appearance, color in particular, are somewhat variable and dependent on growing conditions.
For example, specimens growing on logs in oak and hickory forests in the spring tend to have more yellowish-white, depressed caps than those found in the same location in autumn, which are light yellow brown and more convex in shape.
The fruit body development of M. rotula is hemiangiocarpous, with an hymenium that is only partially enclosed by basidiocarp tissues.
Robert Kühner showed that a cortina-like tissue covers the young gills before the expanding cap breaks away from the stem.
In unfavorable weather conditions, the mushrooms may fail to develop normally and instead produce semi-gasteroid basidiocarps.
The cap of the fruit body is thin and membranous, measuring 3 to 20 mm (0.1 to 0.8 in) in diameter. It has a convex shape slightly depressed in the center, conspicuous furrows in an outline of the gills, and scalloped edges. Young, unexpanded caps are yellowish brown; as the cap expands, the color lightens to whitish or light pinkish-white, often with a darker, sometimes brown center. The variety fusca has brown caps.  The white or slightly yellowish flesh is very thin, reaching about 0.25–1.5 mm thick in the central part of the cap, and even thinner at the margin.
Gills are attached to a collar, never to the stem, although some specimens have the collar pressed close enough to it that this characteristic may be less obvious. Widely spaced, they have the same whitish to pale yellow color as the flesh, and typically number between 16 and 22. They are initially narrow, but thicken downward to about 1–3 mm at the exposed edge. The stem is 1.2 to 8.0 cm (0.5 to 3.1 in) long and up to 0.15 cm (0.06 in) thick, with a smooth, sometimes shiny surface. It is tough, hollow, and either straight or with some curving. The color is blackish-brown up to a lighter, almost translucent apex. The base of the stem may be connected to dark brown or black root-like rhizomorphs 0.1–0.3 mm thick. Mature specimens display no veil.
Details of the fruit bodies' appearance, color in particular, are somewhat variable and dependent on growing conditions. For example, specimens growing on logs in oak and hickory forests in the spring tend to have more yellowish-white, depressed caps than those found in the same location in autumn, which are light yellow brown and more convex in shape. The fruit body development of M. rotula is hemiangiocarpous, with an hymenium that is only partially enclosed by basidiocarp tissues. Robert Kühner showed that a cortina-like tissue covers the young gills before the expanding cap breaks away from the stem. In unfavorable weather conditions, the mushrooms may fail to develop normally and instead produce semi-gasteroid basidiocarps.
Marasmius rotula