Family Description:
Most members of this family have an alternation of heteromorphic generations in which the gametophyte is the upright phase we recognize, and the tetrasporophyte is a crust. Gametophytes are flattened and branched or bladelike. Tetrasporangia are zonate and are scattered in the crustose phase. The medulla of the gametophyte is filamentous. Some members of this family were formerly included in the Solieriaceae.

Species description:
Gametophytes of the Red Opuntia grow attached to rocks. A small, discoidal holdfast holds one primary blade, which is flatttened and up to 15 cm (6 in) in diameter, on a stipe up to 8 mm (0.3 in) long. With age, secondary blades proliferate around the edges of the primary blade, and sometimes additional orders of blades also develop. The mature individual is up to 20 cm (8 in) tall and 30 cm (12 in) wide. It is dark red and thick with a rather cartilaginous texture. Superficially, it resembles a Prickly Pear Cactus (Opuntia) in shape, hence the generic name.

The tetrasporophyte of the Red Opuntia is crustose.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Callymenia californica
Cruoria profunda