Family Description:
Most species are flattened and one to six cells thick. Many have veins or a midrib. Tetrasporangia are tetrahedrally divided and usually occur in sori. Cystocarps are embedded in the plant. Carpospores escape through an ostiole.

Species description:
Northern Sea Oak is erect, up to 18 cm (7 in) high, and perennial. In the first year, a single stipe carrying one dark red blade develops. The blade, which has a prominent midrib and oppositely branching veins, reminds us of an oak leaf, hence the common name. The thin blade has a rounded or somewhat pointed tip, the margins are smooth and undulating, and the base is rather wedge-shaped. By the end of the first growing season, the blade has eroded to leave just the midrib, and in the second year, this persistent midrib proliferates several secondary blades, each of which looks similar to the single blade of the first year. Eventually, the main axis measures up to 2 or 3 mm in diameter, and internally it contains bundles of rhizoids (these cannot be seen externally, however). The main axis acquires a cartilaginous texture over time.

Tetrasporangia are scattered over the surfaces of the blades between the veins. The cystocarps form as hemispherical bumps on midribs and side veins of the blades.

This genus is named in honor of Jun Tokida, a Japanese phycologist at Hokkaido University in Hakodate, who studied the seaweeds of northern Japan and southern Saghalien.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Tokidadendron kurilensis