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

Family Description:
In most members of this family, the intercalary meristem at the junction of the stipe and blade is split so that the stipe itself is branched, and there are numerous terminal blades. Midribs are lacking. Sori usually develop on blades or on sporophylls that develop from the blade side of the meristem rather than the stipe part as in the Alariaceae. This family contains the giant kelps, and many members of the family have pneumatocysts (gas-filled floats). This family contains Lessonia, Macrocystis, Nereocystis, Pelagophycus, Postelsia and possibly Ecklonia, Egregia and Eisenia.

Species description:
Another impressive kelp, Feather Boa has perennial sporophytes up to 15 m (49 ft) in length but usually much shorter. These are dark brown to olive greenish in color. Feather Boa is anchored by a massive, branched holdfast up to 25 cm (10 in) in diameter. This holdfast produces a single stipe that is quite flattened and 1 to 3.5 cm (0.4 to 1.4 in) in diameter. The stipe is decorated with tiny papillae each up to 3 mm (about 0.1 in) in length. It is irregularly branched near its base, producing up to two dozen long branches. The sides of these stipe branches carry a dense (in the northern part of its range) to sparse (in the southern part) fringe of small blades up to 8 cm (3 in) in length. Each of these small blades tapers to a narrow constric ion at its base where it joins the stipe branch. Some blades develop as ellipsoid pneumatocysts (air bladders), whose function is to hold the blades erect in the water column so that they can reach the sunlit layers above. Some other lateral blades serve as sporohylls; they become completely covered with microscopic sporangia (spore-forming organs). These sporophylls, which are shorter and narrower than sterile blades, are scattered among the latter. Sporangia can mature at any time during the year, but do so most abundantly from spring to fall. The sporophylls tend to be smooth in the northern part of the range of this species but wrinkled in the southern part.

Feather Boa grows on rocks and often grows with Macrocystis. Throughout much of its range it serves as habitat for the tall-shelled Seaweed Limpet (Tectura insessa), which feeds on the superficial tissues of the Feather Boa and also on its epiphytes.