ROYAL FERN, in botany, the common name for the fern Osmunda regalis, a native of Britain, where it grows in bogs, marshy woods, &c. It is a handsome plant with bi-pinnate fronds 2 to 6 ft. long and 1 ft. or more broad; the tops of the fronds are fertile, the fertile pinnae being cylindrical and densely covered with the spore-cases, giving the appearance of a dense panicle of flowers, whence the plant is known as the flowering fern. There are various cultivated forms—cristata has the ends of the fronds and the pinnae finely crested, and corymbifera has curiously forked and crested fronds. Several other species, such as O. cinnamomea, O. Claytoniana, are known as handsome greenhouse ferns (see also Ferns).