In the western region of the contiguous United States the Ophioglossaceae are represented by three species of Ophioglossum and twenty-two described species of Botrychium. In the latter there are twenty species in the moonwort subgenus Botrychium, B. multifidum in the grapefern subgenus Sceptridium and B. virginianum, the rattlesnake fern, in the subgenus Osmundopteris. This region supports the greatest number of moonwort species in the world, including at least two species as yet undescribed. Because of morphological diversity within species and sometimes subtle differences between species, the moonworts present challenging taxonomic problems. A number of Ophioglossaceae species are listed as endangered, threatened or of special concern in one or more states. Special problems regarding the conservation of rare Ophioglossaceae in the western US are discussed.

Key words: Botrychium, conservation management, moonwort, Ophioglossaceae, Ophioglossum