It produces small stemless fruit bodies that grow on the rotting wood of the flowering tree koa.

Desjardin and Hemmes consider the fungus best classified in Rolf Singer's section Neosessiles of the genus Marasmius.

[1] The fruit bodies of Marasmius koae are rounded and fan-shaped to hemispherical, measuring 0.3–1.0 cm (0.12–0.39 in) in diameter.

The cap surface is dull and dry, grooved, and has a texture ranging from smooth to somewhat velvety.

[1] The thin-walled spores are somewhat fusoid (spindle-shaped) to elongated ellipsoidal in shape, smooth, hyaline (translucent), and measure 12–14.5 by 4–4.8 μm.