The Aleutian shield fern is the only native plant of Alaska on the federal endangered species list. As there are fewer than 150 plants known to exist, it is a very rare North American plant. It was listed as endangered in 1988.Polystichum aleuticum was first described in 1938, but it could not be located again until 1975 when a group was identified on Mount Reed on Adak Island. A second, third, and fourth population, all on Mount Reed, was located in 1988, 1993, and 1999, respectively. Searches on other Aleutian Islands since 1988 have failed to identify additional populations.Polystichum aleuticum, the Aleutian holly fern or Aleutian shield fern, is an endangered species of the Polystichum genus and currently consisting of a small, vulnerable population endemic found only on Adak Island, Alaska, a remote island of the Aleutian Islands chain in the northern Pacific Ocean. In 1992, 112 specimens existed in the wild, and a recovery plan was implemented.
It is unlike any other known shield fern found in North America, and originally it was questioned whether it even belonged to the Polystichum genus. However, it was found to be similar to a dwarf Polystichum species located in the southwestern mountains of Asia.
The Polystichum aleuticum fern is described as erect and approximately six inches tall. It usually found growing alone, rather than in groups. It has a fibrous root with dead leaf remnants attached. Its leaves, visible during the growing season, are light or dark olive green, and tapering. Each of its fronds has 15 to 25 pairs of leaflets (pinnae) that are either sessile or have short stalks and are 4 to 8 mm in length. The upper leaflets each have one spore-producing sori (sometimes two) on the leaflet under surface that is protected by the indusium, a flap of tissue. The spores are produced in July and August.