The cap is initially convex, but as it matures, it expands to a bell-shape, typically reaching 0.3 to 1 cm (0.1 to 0.4 in) in diameter.
The cap sometimes has a small abrupt umbo (a central bump), and the cap margin is pressed closely against the stem when young, often flaring or curving slightly inward.
As the cap expands, a narrow sterile (i.e., without any reproductive cells typical of the hymenium) band which frequently becomes lobed or irregularly-jagged often forms at the extreme margin.
The cap surface is smooth, faintly translucent-striate when moist, at first pruinose but soon naked.
The color is red when young, soon becoming yellowish toward the margin, and slowly fading to bright orange-yellow.
The flesh is thin, brittle, yellow, and has no distinctive odor or taste.

The gills are adnate (with gills broadly attached to the stem, slightly above the bottom of the gill, with most of the gill fused to the stem) or slightly rounded next to the stem.
The individual gills are close to subdistant, with between 10–14 reaching the stem, and two or three tiers of lamellulae (short gills that do not reach the stem).
The gills are moderately broad, pale orange to whitish, often yellowish at the base and whitish along the edges.
The stem is 1 to 6 cm (0.4 to 2.4 in) long, and up to 1 mm thick; flexuous (winding from side to side), brittle, with the base covered with sharp, straight, and stiff white hairs.
The surface is densely white-pruinose initially, but soon becomes naked with a subsequent color shift to orange-yellow or lemon yellow.
This species has been described as "a delight to behold", but "one usually has to get down on hands and knees to find it!"

The fruit bodies of Mycena acicula are considered inedible, as they are too small and insubstantial to be considered for consumption.
The cap is initially convex, but as it matures, it expands to a bell-shape, typically reaching 0.3 to 1 cm (0.1 to 0.4 in) in diameter. The cap sometimes has a small abrupt umbo (a central bump), and the cap margin is pressed closely against the stem when young, often flaring or curving slightly inward. As the cap expands, a narrow sterile (i.e., without any reproductive cells typical of the hymenium) band which frequently becomes lobed or irregularly-jagged often forms at the extreme margin. The cap surface is smooth, faintly translucent-striate when moist, at first pruinose but soon naked. The color is red when young, soon becoming yellowish toward the margin, and slowly fading to bright orange-yellow. The flesh is thin, brittle, yellow, and has no distinctive odor or taste.
The gills are adnate (with gills broadly attached to the stem, slightly above the bottom of the gill, with most of the gill fused to the stem) or slightly rounded next to the stem. The individual gills are close to subdistant, with between 10–14 reaching the stem, and two or three tiers of lamellulae (short gills that do not reach the stem). The gills are moderately broad, pale orange to whitish, often yellowish at the base and whitish along the edges. The stem is 1 to 6 cm (0.4 to 2.4 in) long, and up to 1 mm thick; flexuous (winding from side to side), brittle, with the base covered with sharp, straight, and stiff white hairs. The surface is densely white-pruinose initially, but soon becomes naked with a subsequent color shift to orange-yellow or lemon yellow. This species has been described as "a delight to behold", but "one usually has to get down on hands and knees to find it!"
The fruit bodies of Mycena acicula are considered inedible, as they are too small and insubstantial to be considered for consumption.
Mycena acicula