Family Description:
Most members of this family are flattened blades; they can have single, entire blades or be much-branched. The blades can be smooth or covered with short protuberances called papillae. Like other red algae, the characters that unite this family are details of the female reproductive apparatus and post-fertilization development. Tetrasporangia are cruciate and occur in internal sori.
Although members of this family have an alternation of isomorphic generations, the two generations have different cell wall carbohydrates. When extracted, the carbohydrates of the gametophyte form a gel whereas those of the tetrasporophyte form a viscous liquid. These carbohydrates represent two different forms of carrageenan, an additive to most ice creams to keep them smooth, and to chocolate milk to keep the chocolate in suspension.

Species description:
This is an especially large species of Mazzaella; blades can reach 120 cm (almost 4 feet) tall or even taller, on stipes up to 6 cm (2.4 in) long, but usually much shorter. The blades are thick and dark purple when wet, but when they dry during low tide they can turn brown or even black, depending on the phase. Each blade is elongate or broadly ovate, sometimes with a terminal cleft, and tapers to a wedge-shaped or heart-shaped base. Blades broader than tall are not uncommon in sheltered areas.

Researchers working near Vancouver, British Columbia, have shown that gametophytes of this species are more abundant than tetrasporophytes in summer, a time when gametophytes exploit favorable environmental conditions. In winter, tetrasporophytes (which are better at surviving adverse environmental conditions) are more abundant than gametophytes. These alternate phases are morphologically isomorphic but have walls composed of polysaccharides with different chemical compositions.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Iridaea cordata
Gigartina cordata
Iridaea cordata
Iridaea splendens
Iridophycus cordatum
Iridophycus fulgens
Iridophycus splendens