or Moon-Fern, in botany, the popular name of a small fern (Botrychium Lunaria), belonging to the order Ophioglossaceae (see Ferns). It has a tuberous root-stock and a stout fleshy glabrous frond 3 to 6 in. long, with a sterile and fertile portion; the former bears several pairs of close-set, semi-circular or moon-shaped pinnae, the latter is pinnately branched and covered, on the face opposed to the sterile portion, with small globose spore-cases which burst transversely. It is a widely distributed plant in the north and south temperate and cold zones, and is found in pastures and grassy banks in Britain.