Polystichum aleuticum, the Aleutian holly fern or Aleutian shield fern, is an endangered species of the ''

Polystichum ''Polystichum'' is a genus of ferns in the family Dryopteridaceae, subfamily Dryopteridoideae, according to the Pteridophyte Phylogeny Group classification of 2016 (PPG I). The genus has about 500 species and has a cosmopolitan distribution. Th ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

and currently consisting of a small, vulnerable population

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

found only on

Adak Island Adak Island ( ale, Adaax, russian: Адак) or Father Island is an island near the western extent of the Andreanof Islands group of the Aleutian Islands in Alaska. Alaska's southernmost town, Adak, is located on the island. The island has a lan ...

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

, a remote island of the

Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...

chain in the northern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

. In 1992, 112 specimens existed in the wild, and a recovery plan was implemented. The Aleutian shield fern is the only

native plant In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often popularised as "with no human intervention") during history. The term is equ ...

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 North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...

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

. A second, third, and fourth population, all on Mount Reed, was located in 1988, 1993, and 1999, respectively. Searches on other

since 1988 have failed to identify additional populations.

Distribution

It is unlike any other known shield fern found in North America, and originally it was questioned whether it even belonged to the genus ''

''. However, it was found to be similar to a dwarf ''Polystichum'' species native to southwestern mountains of China and the Himalayas.

Description

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 Fiber or fibre (from la, fibra, links=no) is a #Natural fibers, natural or Fiber#Artificial fibers, artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The stronge ...

root with dead leaf remnants attached. Its leaves, visible during the growing season, are light or dark olive green, and tapering. Each of its

frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...

s has 15 to 25 pairs of leaflets (

pinnae The auricle or auricula is the visible part of the ear that is outside the head. It is also called the pinna (Latin for "wing" or " fin", plural pinnae), a term that is used more in zoology. Structure The diagram shows the shape and location ...

) that are either

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

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 sorus (pl. sori) is a cluster of sporangia (structures producing and containing spores) in ferns and fungi. A coenosorus (plural coenosori) is a compound sorus composed of multiple, fused sori. Etymology This New Latin word is from Ancient ...

, a flap of tissue. The spores are produced in July and August.

Notes

External links

USDA Plant Profile: ''Polystichum aleuticum''Flora of North America — ''Polystichum aleuticum''
{{Taxonbar, from=Q7226977 aleuticum Flora of Alaska Endemic flora of the United States Ferns of the United States ~ Critically endangered flora of the United States Plants described in 1938