moonwort; a genus of the order of filices, belonging to the cryptogamia class of plants. There are several species; the most remarkable of which is the regalis, omdun-royal, or flowering fern. This is a native of Britain, growing in putrid marshes. Its leaf is doubly winged, bearing bunches of flowers at the ends. The root boiled in water is very slimy; and is used in the north to stiffen linen instead of starch. Some of the leaves only bear flowers.