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

Family Description:
Blades are undivided; they have a central midrib or thickening, and are borne on a simple or dichotomously branched stipe. Sori occur on sporophylls, which develop in opposite rows along the stipe near the intercalary meristem at the junction of stipe and blade. As currently constituted, the family contains only three genera: Alaria, Pterygophora, and Lessoniopsis. The last two genera are monotypic; that is, they consist of only a single species each.

Species description:
The sporophyte of Strap Kelp is the conspicuous generation in the life cycle, as in other kelps. It is perennial, dark brown to almost black, and up to 2 m (6.6 ft) tall. The huge, somewhat conical holdfast is composed of repeatedly branched haptera and measures up to 15 cm (almost 6 in) across. This supports several tough, almost woody, solid, cylindrical stipes that branch repeatedly. Each stipe branch, which is up to 8 mm (0.3 in) in diameter, carries a single, narrow, unbranched blade up to 1 m (39 in) long and 12 mm (0.5 in) wide. There can be up to 500 of these blades on an individual. Older blades have a flattened midrib about 3 mm (0.1 in) in diameter.

Sporophylls do not develop midribs; they are shorter and a little wider than the sterile blades. Sori (patches of spore-producing organs) occur on these sporophylls. Pneumatocysts are lacking.

Strap Kelp prefers to grow on rocks in extremely exposed situations where it is subjected to heavy surf.