Family Description:
Plants have branches arising radially along the entire length of the solid, cylindrical axes. Some branches are leaflike, with a midrib and smooth or toothed margins. Branches arising from the main axis can have blades immediately below them. Each axis is terminated by a single, three-sided apical cell. Pneumatocysts occur singly and terminate the branches on which they occur (that is, they are not intercalary). A single egg is produced in each oogonium.

Species description:
Wireweed is a rather tough and wiry species that is branched and bushy. It is anchored by a discoidal holdfast. The main axes arise near the base, but each main axis branches alternately in turn and carries small blades. The elongated blades are rather lanceolate with toothed margins; they are longest near the base of the plant where they can be up to 10 cm (4 in) in length, and become smaller towards the tips of the branches where they can be only a few millimeters (less than 0.3 in) long. The stems and blades are golden brown. It grows to 2 m (6.5 feet) tall.

Small floats, called vesicles, occur singly or sometimes in small clusters, and occupy the blade axils (the angle between the blade and the stem immediately above it). These vesicles are only about 2 mm (less than 0.1 in) in diameter and can be a little paler in color than the rest of the organism. They are round and do not have a pointed tip, in contrast to those of Cystoseira geminata, a similar but uncommon species of our outer coast.

Receptacles also arise in blade axils; they are cylindrical or forked and about the same size as the vesicles. In California, some individuals are fertile all year. In colder parts of the North Atlantic, receptacles develop mainly when the water temperature exceeds 10°C (50°F). The fertilized eggs develop into germlings before they are released. Lateral branches can detach and disperse during germling release, helping to disperse the species. After germlings are released they sink and usually quickly attach to rocks near the parent. Since each mature individual is bisexual and self-fertile, it is easily introduced into other areas. When this occurs, it can build up its populations rapidly, especially since it can be fertile throughout much of the year and each individual produces so many receptacles. Another key to the success of this species is that it tolerates water of decreased salinity (as low as 8.5 parts per thousand).

The distribution of this highly invasive species is patchy and spreading. It is not endemic (native) to North America, but was introduced from Japan on shells with oyster spat. Wireweed is thought to have been introduced in the 1930's in Puget Sound, Washington, and has been spreading north and south ever since. We do not know when it reached Southeast Alaska, but we have seen it on rocks in the low intertidal zone in moderately protected waters near Edna Bay, Kosciusko Island, in 1994. It also occurs along the west coast of Prince of Wales Island and adjacent islands, and is particularly lush in Sea Otter Sound. To the south, Wireweed spread to 100 km (62 miles) south of the United States border into Mexico in 1973 and then to Bahia Tortugas on the Baja California Peninsula (about half way to its southern tip) by 1988. Wireweed was introduced into the North Atlantic as well, and was first discovered there in 1973.

Wireweed can withstand at least one week of exposure to water 28°C (83°F) in temperature, and is among the most thermally tolerant of local species of brown algae.

An important predator of Wireweed is the grazer, the Green Sea Urchin (Strongylocentrotus droebachiensis) in the Strait of Georgia, British Columbia, and probably elsewhere as well.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Sargassum kjellmanianum