Dryopteris expansa, the alpine buckler fern, northern 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. Description It has a stout, woody, creeping or ascending stock with large, green lacy fronds typically and rarely long. The deltate fronds are bipinnate at the base, pinnate toward the apex. 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. It is easily confused with the related Dryopteris dilatata (broad buckler fern), differing in the usually smaller fronds, and in the pale brown scales on the frond stem being more uniform in color, rarely having a dark central stripe. It also differs in cytology in having 2n = 82 chromosomes (164 in D. dilatata). Leaves of D. expansa are very similar to those of D. arguta. The species name of this fern, expansa, is from the Latin expando, meaning "to spread out, spread apart, to expand". Other common names include northern wood fern, arching wood fern, spiny wood fern and crested wood fern. Uses The root contains filicin, a substance that paralyses tapeworms and other internal parasites and has been used in herbal medicine as a worm expellent. References External links Flora Europaea. Dryopteris expansa Flora of North America Dryopteris expansa Plants For A Future: Dryopteris expansa expansa Ferns of Asia Ferns of Europe Ferns of the Americas Ferns of the United States Ferns of California Flora of Ontario Flora of Canada Plants described in 1825