Linnaeus named this plant Osmunda lunaria in 1753 and Olof Swartz gave the present name in 1800. This Botrychium, rare in Colorado, is found in most western states; it is the most common of all of the Moonworts shown in this slide show and is the only Moonwort found in the British Isles. 

"Lunaria", Latin, is for the lunar-like shape of the pinnae on the plant and probably also for the shape of the leaves.