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:
A profusely branched holdfast anchors this species to rocks. A single rather flattened stipe up to 1.5 cm (over 0.5 in) wide and of variable length up to 65 cm (about 25 in) is embellished with numerous fine longitudinal striations. This stipe supports a single yellowish-brown to chocolate-brown undivided, oval blade. The blade carries five or seven parallel ribs (no other local alga has this distinctive feature), and these project alternately above and below the surface of the blade. The blade is profusely wrinkled or puckered between these ribs, hence the common name since it resembles seersucker fabric. The blade measures up to 2 m (about 6.5 feet) long and 35 cm (about 14 in) wide.

This species is quite common both in inshore waters and on the outer coast. Sea urchins are among its most important grazers.

Seersucker is usually an annual (but in some areas, it can be perennial). Blades reach their peak of development in our area by the end of May, and within a month they are tattered and sickly looking and definitely past their prime for the season. The species is low in caloric value (2.94 Calories per gram of dry weight).

In British Columbia, Seersucker individuals on the exposed west coast of Vancouver Island have narrower, thicker and more strap-like blades than individuals in more protected places such as near Vancouver. Individuals from exposed sites in southern British Columbia/northern Washington can withstand immersion in water at 20°C (68°F) for a week, but die at higher temperatures.
Recent molecular studies have shown that Costaria is closely related to Laminaria.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Costaria mertensii
Costaria turneri
Laminaria costata