WESTERN SWORD FERN (Polystichum munitum)

Sword Fern
Western Sword Fern
Source: http://www.wildflower.org/gallery/result.php?id_image=16819

Taxonomic Hierarchy:
Kingdom - Plantae
Subkingdom - Tracheobionta
Division - Pteridophyta
Class - Filicopsida
Order - Polypodiales
Family - Dryopteridaceae
Genus - Polystichum
Species - Polystichum munitum 

The Western Sword Fern is known as the "king of northwest ferns." Other common names include the Christmas Fern and the Sword Holly Fern. It is widespread amongst damp woods, usually below 2,000 feet and is most commonly located along the west coast of southeast Alaska to Santa Barbara County in California. This particular indigenous species of sword fern is also found eastward through Washington, in northern Idaho, and up into northwestern Montana. There are few populations, however, that can be found in South Dakota and on Guadalupe Island off of Baja, California. There are also populations located in British Columbia and the fern is common west of the Coast Mountains and on the Queen Charlotte Islands.

Western Sword Fern Distribution
Distribution map of the Western Sword Fern.
Source: http://www.plants.usda.gov/java/profile?symbol=POMU

It can be identified by its evergreen ground cover. It has horizontal stems with reddish-brown scales that grow underground called rhizomes, with bunches as big as 75 to 100 leaves.  It can be found in various environmental conditions, although it prefers shady to partly shady and dry to moist areas. The plant has sword-shaped fronds, hence its name. These pennae, referring to the individual leaves of the fronds, are sharp and serrated, and can grow from 20 to 72 inches long (50 to 180 centimeters). The individual fronds stay attached to their rhizome even after they have withered.

On the back of the fronds, you will find groups of sori called sporangia which produce spores. These spores are created by meiosis and in many ferns the sporangia have approximately 32 to 64 spores that are used for reproduction purposes. Due to the alternation of generations, these spores assist in the fern’s reproduction both sexually and asexually. The two stages in which the Western Sword Fern goes through in order to reproduce are the Sporophyte Generation and the Gametophyte Generation. The former generation refers to the spores germinating themselves asexually to create gametes, mature reproductive cells, while the latter involves the sexual fertilization between the male and female gametes that are produced in the first stage or generation. After this fertilization occurs, the Western Sword Fern returns to its more dominant form of asexual reproduction (Sporophyte Generation).

Spores on the back of Western Sword Fern fronds.
Source: http://www.plants.usda.gov/java/largeImage?imageID=pomu_001_ahp.jpg

Some relatives to the Western Sword Fern are the Anderson's Sword Fern (Polystichum andersonii) which is a hybrid between the Western Sword Fern and the Kwakitutl's Holly Fern (Polystichum kwakiutlii). Another smaller relative is the Imbircate Sword Fern (Polystichum imbricans) that can be found in British Columbia and south towards California. This particular species of sword fern prefers drier habitats than the Western Sword Fern. The Imbricate Sword Fern also produces fronds with overlapping pinnae, similar to that of the Shasta Holly Fern (Polystichum lemmonii).

As far as human use, the Western Sword Fern is often planted in gardens and is used for ground cover, although many people believe it to be too fragile when in fact is tougher than it seems. This particular species of fern is also used for decoration. For example, every year, large amounts of the Western Sword Fern are shipped from the northwest to various locations around the country to be made into Christmas wreathes. (This is why another one of its common names is the Christmas Fern). It would be considered helpful because it can be used for medicinal purposes such as relieving the pain caused by Stinging Nettle. The Western Sword Fern has also been planted in certain forest areas in an effort to maintain particular growth reserves. The human impact on some forest areas is such that recreational activities, such as camping and hiking, are destroying the other forest life that resides there. By planting sword ferns, people are discouraged from off-trail use.

Indigenous tribes are known to consume the Western Sword Fern for various purposes. For example, they cook the rhizomes and eat them to cure diarrhea. When the leaves of the sword fern are young, the Swinomish would eat them to ease the pain of sore throats and tonsillitis. Women of the Lummi tribe would chew the leaves of this particular sword fern to help them during childbirth.  The leaves themselves can also be used for flooring, bedding, and protective layers in food or storage boxes and baskets. It is believed that deer and elk will consume this particular fern, although it is suspected that it does not taste very good because of the rough texture of its leaves.

There do not seem to be any direct symbiotic relationships between the Western Sword Fern and other organisms, nor does it play an especially particular role in its habitat. The uses mentioned in the above two paragraphs demonstrate its primary purposes. However, the Western Sword Fern is considered to be an invasive species in some areas such as Florida. In that state, it is classified as a "Category 1 invasive species" and agricultural experts are attempting to get rid of the fern because they believe it to be a threat to native plant species of Florida.

I chose to focus on the Western Sword Fern because it is found on the Western Oregon University campus and it is a very distinguishable non-flowering plant. It grows abundantly, covering the ground and the particular population that I took a sample from on campus not only grew over a large amount of surface area but grew quite high as well. The fact I found most interesting about the Western Sword Fern was how it has two stages of reproduction and reproduces both sexually and asexually. It is also interesting how many various human uses there are for the Western Sword Fern, ranging from decorations to its consumption by indigenous tribes.


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