Polystichum aleuticum
Encyclopedia
Polystichum aleuticum, the Aleutian Shield Fern, is an endangered species
of the Polystichum
genus
and currently consisting of a small, vulnerable population endemic and existing 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.
The Aleutian Shield Fern is the only native plant
of Alaska on the federal endangered species list. As there are less 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
; further searches on other Aleutian Islands failed to identify additional populations.
genus. However, it was found to be similar to a dwarf Polystichum species located in the southwestern mountains of Asia.
s 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.
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of the Polystichum
Polystichum
Polystichum is a genus of about 260 species of ferns with a cosmopolitan distribution. The highest diversity is in eastern Asia, with about 120 species in China alone; the region from Mexico to Brazil has nearly 100 additional species; Africa , North America , and Europe have much lower diversity...
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and currently consisting of a small, vulnerable population endemic and existing only on Adak Island
Adak Island
Adak 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...
, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, a remote island of the Aleutian Islands chain in the northern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
. In 1992, 112 specimens existed in the wild, and a recovery plan was implemented.
The Aleutian Shield Fern is the only native plant
Native plant
Native plant is a term to describe plants endemic or naturalized to a given area in geologic time.This includes plants that have developed, occur naturally, or existed for many years in an area...
of Alaska on the federal endangered species list. As there are less than 150 plants known to exist, it is a very rare North American
North American
North American generally refers to an entity, people, group, or attribute of North America, especially of the United States and Canada together.-Culture:*North American English, a collective term used to describe American English and Canadian English...
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
Adak Island
Adak 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...
; further searches on other Aleutian Islands failed to identify additional populations.
Distribution
Polystichum aleuticum, the Aleutian Shield Fern, may be the least known of all the world's ferns as there is little information available. It is unlike any other known shield fern found in North America, and originally it was questioned whether it even belonged to the PolystichumPolystichum
Polystichum is a genus of about 260 species of ferns with a cosmopolitan distribution. The highest diversity is in eastern Asia, with about 120 species in China alone; the region from Mexico to Brazil has nearly 100 additional species; Africa , North America , and Europe have much lower diversity...
genus. However, it was found to be similar to a dwarf Polystichum species located in the southwestern mountains of Asia.
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 root with dead leaf remnants attached. Its leaves, visible during the growing season, are light or dark olive green, and tapering. Each of its frondFrond
The term frond refers to 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...
s has 15 to 25 pairs of leaflets (pinnae) that are either sessile
Sessility (botany)
In botany, sessility is a characteristic of plants whose flowers or leaves are borne directly from the stem or peduncle, and thus lack a petiole or pedicel...
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.