Plants are flattened, strap-shaped and dichotomously branched, or cylindrical with compressed laterals. Growth in this family occurs by means of a single four-sided apical cell. One, two, four or eight eggs are produced in each oogonium, depending on the genus.
Dwarf Rockweed is perennial and up to just 8 cm (3 in) tall, which suggested this common name to us. Like Rockweed, to which it is closely related, Dwarf Rockweed is dichotomously branched (that is, it lacks a central axis), and the branches lie mostly in one plane. Unlike Rockweed, however, Dwarf Rockweed branches lack midribs. The stout, lobed holdfast ultimately bears many erect branches that branch three to five times. Towards the base of the seaweed, the branches are quite cylindrical, but above this they become mostly flattened. Each branch is only 2 to 4 mm (about 0.1 to 0.2 in) wide. Mature branch tips develop simple or forked, warty and inflated receptacles 5 to 10 mm (0.2 to 0.4 in) in length. As in related species, the warts surround openings into chambers (the conceptacles) that contain the microscopic, gamete-producing organs. Both male and female organs can be found on a single seaweed, and each female organ produces a single, functional egg cell.
Dwarf Rockweed prefers to grow on the upper surfaces of rocks in areas subject to strong surf.
Source: North Pacific Seaweeds