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:
Scuba divers are familiar with the impressive Dragon Kelp, an important canopy-forming subtidal species in the northern part of the area covered by this book. Specimens to 25 m (82 ft) in length have been measured. This massive kelp is dark brown in color and has a vegetative blade (which does not carry reproductive organs) with a distinct midrib 2 to 3 cm (0.8 to 1.2 in) wide. The midrib is hollow, and bears scattered swollen blisters or gas-filled chambers (hence "fistulosa") that hold the blade up into the upper layers of the water column in order to facilitate photosynthesis. Dragon Kelp is anchored to rocks by a large and much branched holdfast. Between the holdfast and the vegetative blade is a stipe 20 to 25 cm (8 to 10 in) in length and 0.8 to 1.2 cm (0.3 to 0.5 in) in diameter. The stipe is basally cylindrical, but below the vegetative blade it flattens to form a rachis where it carries a variable number of specialized reproductive blades (sporophylls) laterally. The sporophylls of mature individuals are crowded with microscopic, spore-forming organs (sporangia).

Dragon Kelp can often be found growing intermingled with Bull Kelp (Nereocystis luetkeana).