Family Description:
Most members of this family are flattened and branched or bladelike. They have an alternation of isomorphic generations. Cells of the female reproductive apparatus are relatively large and often lobed. Tetrasporangia are scattered in the outer cortex and are cruciately divided.

Species description:
The annual blades of Red Sea-leaf are dark red to purple. Young blades are undivided and have pointed tips; they have a strong midrib and forked lateral veins running out to the blade margins. After they reach their mature size of about 50 cm (20 in) or more in height and 8 cm (about 3 in) in width, the blades often have a branch or two (northern specimens tend to be smaller). With increased age, the blade becomes tattered and damaged by the surf. Small papillae associated with reproductive structures appear late in the season on the remaining blade surfaces and on the persistent midribs and veins. Several blades can arise from the same discoidal holdfast.

Red Sea-leaf can be found growing on rock in exposed locations.

Source:  North Pacific Seaweeds