Sword-Fern (Polystichum munitum)

This text was originally published in Coastal Grower (formerly The Island Grower) in Victoria, British Columbia. For subscription information, please call Susanne Steele at the Coastal Grower at 250-478-0825.

British Columbia's moist and mild coastal climate provides ideal conditions for ferns to thrive, so much so that several fern species are obvious and characteristic components of the conifer forest floor. Most abundant of all these ferns is the stately and lush sword-fern of the Polypody Family (Polypodiaceae).

Sword fern grows as a large perennial clump of leaves from a massive crown. The crown consists of a woody mass of rhizomes (root-stems) buried in reddish brown scales. Roots explore the soil from the rhizome. In a mature well-established clump the mass of the crown may reach half a metre or more in diametre.

Dark evergreen sword-fern fronds stand stiffly from the crown. Fronds reach as tall as 1.5 metres (60") and up to 25 cm (10") wide. The lower third of the frond consists of a densely scaly brown stipe. The upper two-thirds or blade has numerous narrow, pointed and toothed leaflets. Near the tip of the frond the leaflets become progressively shorter. Young unfolding leaves are at first curled like a shepherd's crook or crozier, then gradually unfurl and expand.

Ferns are not flowering plants, they reproduce by spores which are microscopic pollen-grain like bits of plant material. Spores form in sporangia, tiny thin-walled sacs full of spores. The sporangia of sword-fern cluster in brown dot-like structures called sori (the singular is called sorus), which line the back of each leaflet of the frond. These many (polys in Greek) lines (stichos in Greek) of sori give rise to the scientific name Polystichum. The species name munitum = armed derives from the numerous teeth along the leaflets.

Sporangia split open and the spores drift to the ground where they germinate only if it is moist. The spores grow into frail gametophytes with only half the genetic array of the parent. Male and female structures occur on the gametophytes and male sperm swims to fertilize the female egg. Once fertilized the egg develops into a proper leafy fern plant.

In British Columbia sword-fern is dominantly a coastal species, occurring more than two thirds of the way to the Yukon border. The range extends across extreme southern B.C. and adjacent Washington and Idaho into moist settings in the southeastern part of the province. The North American range extends along the coast from Alaska almost to the Mexican border. Generally sword-fern thrives in the shaded humus of the damp to moist conifer forest floor. In very wet forests you may see it perched on a shady rock face. Sword-fern forms a distinctive association with western red cedar (Thuja plicata) on nutrient rich seepage sites. Fern clumps completely cover the forest floor, in a manner somewhat reminiscent of a lush tropical jungle. A stiffer narrow-leaved species of sword-fern, called imbricate sword-fern (Polystichum imbricans) grows among boulders and in rock crevices in dry usually open settings.

Aboriginal British Columbians used sword-fern for various purposes. In spring rhizomes were dug up, cleaned and cooked in open fires or pits. Cooked rhizomes were then peeled and eaten usually with grease or salmon eggs. The fronds were used to line pits for cooking root foods and to line boxes and baskets. Fern fronds also provided a decorative motif for basket designs.

Sword-fern is among the easiest ferns to grow in the garden. Since this fern is so ubiquitous in coastal lowland sites, many suburban building lots come with their own supply. If possible it's best to leave the clump where it sits, making sure there is shade. However the plants transplant readily and many can be easily rescued from development projects. Sword-fern is one of the more widely available native species, so ask a local garden centre or nursery to order it in if you cannot get it from a fiend or rescue site. Spores spread in a moist and shaded site will yield plants in a few years too.

For best results, choose a shaded to partly open moist setting. In the Native Plant Garden at the Royal BC Museum we use it in a mass planting under trees between two buildings. Suits this situation much better than lawn. Sword-fern is ideal for a woodland garden, establishing a lush verdant framework for the garden's further development. Once established the only care the fern needs is to remove unsightly dry fronds in the winter.

Try ferns in your garden; many of them are well suited for the those difficult shaded sites. Ferns also illustrate how less advanced plants reproduce without flowers. Visit the Native Plant Garden at the Royal British Columbia Museum and see luxuriant clumps of sword-fern and other fern species.

For more information, contact Richard Hebda at the Royal BC Museum.