Gymnocarpium dryopteris (western oakfern, common oak fern, oak fern or northern oak fern) is a fern of the family Cystopteridaceae. It is widespread across much of North America and Eurasia. It has been found in Canada, the United States, Greenland, China, Japan, Korea, Russia, and most of Europe. Gymnocarpium dryopteris has small, delicate fronds up to 40 cm (16 inches) long, with ternately-compound pinnae (leaves). Fronds occur singly. On the underside of matured pinnae with naked sori can be found. The species grows in coniferous woodlands and on shale talus slopes. Gymnocarpium dryopteris, a forest understory plant, is not found in association with Quercus (oak).