E-Flora BC: Electronic Atlas of the Flora of British Columbia

Family Description:
Members of this family have a single, terminal blade that is divided in some species. The stipe is rarely branched. Blades are smooth or undulate, entire or with holes, of uniform thickness or with a central, thickened region (midrib). Sori develop directly on the blades.

Species description:
The sporophyte is medium to dark brown. It has a well branched holdfast that gives rise to a single, erect, unbranched and somewhat rigid stipe up to 80 cm (2.7 ft) long and about 2 cm (0.8 in) in diameter. This stipe supports a flat blade that is up to 80 cm (31 in) long and 25 cm (10 in) wide. The blade is divided into several to many distinctive, narrow straps and is basally rounded to wedge-shaped.

If thin cross sections are cut from the stipe with a sharp knife or razor blade, concentric rings can be seen. These rings are deposited annually and can therefore be counted to determine both the ages of individuals and the age structure of populations. However, this technique destroys the plants. When this technique was used at exposed and more protected sites in Barkley Sound on the west coast of Vancouver Island, British Columbia, researchers found that young individuals were more abundant in the exposed population while the more protected population contained more evenly spread age classes. This probably reflects more frequent removal of individuals by storms in more exposed locations. They also showed that individuals at the more exposed site were taller and had thicker stipes than individuals of the same age at more protected sites.

This species is usually encountered in bands or extended patches on exposed coasts, and grows on rocks. It has been reported to grow optimally between 10° and 15°C (50° and 58°F), but when water temperatures increase to 17°C (63°F) reproduction is inhibited.