Overview
The Aleutian shield fern is the only endangered plant species found in Alaska. It grows to about 6 inches tall with dark green fronds, or leaves, and tooth-edged pinnae, or leaflets. These tiny ferns grow on a single island, Adak, of Alaska’s Aleutian Islands. All known populations of the Aleutian shield fern are located on Mount Reed, within the Alaska Maritime National Wildlife Refuge. The ferns grow in moist spots in crevices, beneath overhangs, and at the edges of vegetation mats along rock walls.
Though endangered, the Aleutian shield fern may have never been very abundant. Some scientists consider it a “living fossil” left over from the Pleistocene Epoch. Scientists hypothesize that the fern is a polyploid species with hybrid ancestry.
Currently, the few populations on Adak appear stable. Due to their restricted range, they are threatened by earth slides and other unpredictable events that could eliminate the entire species. Human disturbance at this remote location is rare, but hikers and climbers may cause accidental disturbance. In addition, caribou were introduced to Adak in 1958 and may pose a threat.
Currently, U.S. Fish and Wildlife Service staff monitor the fern populations and ensure that potential disturbances from humans or caribou are minimized. The most up-to-date summary of information and threats to the Aleutian shield fern can be found in the 5-year review for the species published in 2019.
Scientific Name
Identification Numbers
Characteristics
Physical Characteristics
The Aleutian shield fern is a small, tufted, solitary plant. The fronds grow to 6 inches (15 centimeters) long and gradually taper above and below the middle. The fronds are only present during the growing season and unfurl as late as August or September.
The stems of the Aleutian Shield Fern are chestnut brown at the base and arise from a stout underground rhizome. The fern’s fronds, or leaves, are dark green and have small pinnae, or leaflets, with toothed edges. Small, straw-colored scales are found on the stem and underside of the leaflets but may be less evident late in the season. The spore masses are aggregated into 6 to 8 patches, also known as sori, forming two rows on the under-surface of the leaf segments as described by B.L. Anderson in 1992.
Habitat
The Aleutian shield fern grows in a narrow microhabitat that consist of rock grottos and moist crevices at the base of steep rock outcrops. All known populations grow on east to northeast facing slopes on the northeast arm of Mount Reed between 1,108 and 1725 feet above sea level as noted by S.L. Talbot and S.S. Talbot in 2002 and later by V. Byrd and J. Williams in 2007.
A level or rolling treeless plain that is characteristic of arctic and subarctic regions with permanently frozen subsoil.
A landmass that projects conspicuously above its surroundings and is higher than a hill.
Environments influenced by humans in a less substantial way than cities. This can include agriculture, silvaculture, aquaculture, etc.
Food
Behavior
Life Cycle
The Aleutian shield fern has the typical life cycle of a fern: a full-grown sporophyte, what is commonly referred to as the fern, produces genetically unique spores. These spores fall and germinate into the gametophyte stage, the prothallus. The prothallus undergoes sexual reproduction to create a new, independent sporophyte.
The life span of this species is unknown.
Investigations into the reproductive biology of Aleutian shield fern were conducted in the 1990s to verify spore viability through germination tests as documented by P.S. Holloway in 1994. A greenhouse population of at least 1,000 mature sporophytes was established in the 1990s. However, difficulty in growing and maintaining a greenhouse population and long-term storage of viable genetic materials have been unsuccessful. Further studies of the ferns on Mount Reed indicate that there is almost complete lack of genetic variation within and between the four known populations of shield ferns as documented by S.L. Talbot and others. This is consistent with a pattern of genetic variation expected if the ferns resulted from a founder event followed by sexual reproduction via selfing.
Similar Species
The Aleutian shield fern may be confused with more common ferns occurring withing its range. Polystichum lonchitis is much taller, growing up to 24 inches, with more robust, thicker, leathery, evergreen leaves and very spiny leaflets. Cystopteris fragilis has more strongly dissected leaflets and lacks scales.
Geography
The first described Aleutian shield fern was from a collection made by Eyerdam in 1932 on Atka Island, Alaska as described by C. Christensen in 1938. However, no ferns have been located on Atka Island since. Today, there are only four known populations of Aleutian shield fern, all located on Mount Reed, Adak Island, Alaska. These four populations are differentiated based on geographic location and not genetics. Most of these shield ferns occur within a narrow microhabitat consisting of rock grottos and moist crevices at the base of steep rock outcrops on east to northeast-facing slopes.
Timeline
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