Polystichum munitum

sword fern

Dryopteridaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Division - Pteridophyta (ferns). Class - Filicopsida. Order - Polypodiales. Family - Dryopteridaceae (wood fern) Genus - Polystichum Roth (hollyfern). Species - Polystichum munitum (Kaulf.) C. Presl (western swordfern).

Ecology: Western sword fern is a relatively large, evergreen, long-lived fern with long fronds arching from a short, scaly, erect rhizome. The sword-shaped fronds are from 50-180 cm and divided pinnately. Individual fronds live for several years and remain attached to the rhizome after withering. The largest leaflets or pinnae are 3-15 cm...Amount of light received influences western sword fern form. Following disturbance that removes the overstory or when plants occasionally establish on rocky outcrops at high elevations, the fronds are dwarfed and more erect.
The light wind-borne spores of ferns enable them to swiftly colonize new sites; however, western sword fern's ability to colonize appears limited by its sensitivity to water stress. On Vancouver Island it is not present during the pioneer stage of floodplain succession. Establishment occurs only under the shelter of a red alder canopy, and its frequency is greatest in the climax community. In the Coast Ranges of Oregon, western sword fern survives disturbances and becomes an important part of the seral vegetation while in the Cascade Range it is of minor importance in early succession.

Identification

This is a refined fern with a massive clump of 3-5 ft., dark-green fronds that resemble a palm tree top cut off. The fronds are evergreen and occur in clumps of 75-100.

Threats

Fire effects: Fire top-kills western sword fern. It can survive intense fire, but aboveground structures may lacking for several years afterwards. Western sword fern has two postfire regeneration strategies. It sprouts from its stout, woody rhizomes. Additionally, a single western sword fern frond may produce millions of light wind-borne spores each year, enabling the species to colonize burn sites. Sites where western sword fern is a major understory species are generally resistant to the effects of fire. On severely burned sites, western sword fern is greatly reduced and recovers slowly over a period of 15 or more years.

Reproduction

Spores are borne in clusters called sori that are found between the midline and the edge of the middle and upper pinnae...Ferns begin to produce spores on a regular, yearly basis when they are between 1 and 5 years of age. From early to midsummer mature ferns produce millions of light, wind-borne spores. Evergreen ferns such as western sword fern may retain some spores over the winter which are released the following spring. The dry spores are very resistant to extreme physical conditions and may remain viable for 2 to 4 years, although their viability and ability to germinate declines with age.

The most important factor in spore germination is sufficient moisture. Temperatures between 15-30 deg C and a slightly acid to neutral pH are generally best for germination. Western sword fern is one of the few fern species which is capable of germination in the dark, although germination is best in the light...When spores germinate, they produce tiny, bisexual gamete-bearing plants (gametophytes) that do not look like the spore-bearing plants. These tiny plants have no vascular system and require very moist conditions in order to survive and enable the sperm to swim to the egg. The spore-bearing plant, which develops in place from the fertilized egg, is initially dependent on the gametophyte but quickly becomes independent.

Vegetative reproduction of western sword fern is limited but can occur through division of its perennial, woody rhizome. The rhizomes are erect and do not spread, although they branch with age.

Species Distribution

Citation

USDA Plant Database
USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov, 4 February 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Flora of North America
Flora of North America Editorial Committee, eds.  1993+.  Flora of North America North of Mexico.  19+ vols.  New York and Oxford.

Intermountain Herbarium
Consortium of Intermountain Herbaria. 2016. http//:intermountainbiota.org/portal/index.php. Accessed on February 04.

Burke Museum Plant Image Collection
The plant image collection at the Burke Museum, University of Washington.

Jepson Manual
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA. $131.95, hardcover; 1600 pages. ISBN-13: 978-0520253124.