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:
At first glance, this looks like a species of Laminaria, but it has a broad, thick midrib up to almost 5 cm (1.75 in) wide (Laminaria lacks midribs). A highly branched holdfast gives rise to a single stipe up to about 50 cm (20 in) long. The cylindrical stipe is about 1 cm (about 0.4 in) in diameter at the base but tapers somewhat upwards. The dark brown blade is about 150 cm (almost 60 in) long and about 28 cm (11 in) wide with little puckers scattered along the blade adjacent to the midrib. The blade lacks holes and is somewhat ruffled at the edges.

The stipe and holdfast are perennial while the blade is annual, making this a deciduous, perennial kelp. On the west coast of Vancouver Island, British Columbia, blades begin to senesce when the water reaches about 14°C (58°F). Individuals are without blades for about two weeks in the fall, after which the new blades begin to form. The abscission zone (where the blade detaches) is located where the blade meets the stipe. In 1982, an El Niño year with atypically high water temperatures (17.5°C, or 64°F) and reduced levels of nitrate and phosphate, blade loss occurred three months earlier than normal. New blades then began to grow, but these were subsequently shed again in the fall. In 1984, the continued lack of nutrients caused decreased growth in this kelp.
Laboratory experiments have shown that Sea Spatula from southern British Columbia/northern Washington State can survive water temperatures to just 15°C (59°F), making it, along with Cymathere, Hedophyllum and Laminaria yezoensis among the most thermally sensitive of any local algae.

The perennial parts of Sea Spatula contain most of the tissue nitrogen, and researchers have speculated that the low amount of nitrogen in the blade in summer might indicate that Sea Spatula has nitrogen-limited growth.

This species is edible and rather low in caloric value (2.76 Calories per gram of dry weight). However, it is scarce enough that one should probably just admire its rare beauty rather than harvest it for a meal. The conspicuous individual is the sporophyte, and spores form in sori all over the surface of the blade.

Sea Spatula prefers to grow in areas where currents are strong.

Source:  North Pacific Seaweeds