Dryopteris expansa, alpine buckler fern or spreading wood fern, is a species of fern native to cool temperate and subarctic regions of the Northern Hemisphere, south at high altitudes in mountains to Spain and Greece in southern Europe, to Japan in eastern Asia, and to central California in North America. The species was first described from Germany. It prefers cool, moist mixed or evergreen forests and rock crevices on alpine slopes, often growing on rotting logs and tree stumps and rocky slopes. It is characteristically riparian in nature, and is especially associated with stream banks. It has a stout, woody, creeping or ascending stock with large, green lacy fronds 10-60 centimeter (rarely 90 centimeter) long. The deltate fronds are bipinnate at the base, pinnate toward the tip. The rhizome is erect or ascending, often producing offshoots. sori occur medially on the underside of the pinnae. Propagation is by spores and vegetatively by division of the rhizome.