Rhodophyceae

Rhodophyceae is a class of algae commonly known as red algae. They are a diverse group of eukaryotic organisms belonging to the phylum Rhodophyta. Red algae are characterized by the presence of phycobilins, pigments that give them their characteristic red or purplish color, although some species can appear green, brown, or even black. These pigments are accessory to chlorophyll a, which is the primary photosynthetic pigment.

These algae are primarily marine, found in a wide range of oceanic environments from intertidal zones to deep-sea depths. While some species are planktonic, the vast majority are benthic, attaching to substrates like rocks, shells, or other algae. A small number of red algae are found in freshwater habitats. Their life cycles are often complex, involving alternation of generations with distinct haploid and diploid phases.

Economically, rhodophyceans are significant. Many species are harvested for food, such as nori (Porphyra spp.) and dulse (Palmaria palmata). They are also a major source of agar and carrageenan, polysaccharides used as gelling agents, thickeners, and stabilizers in food, pharmaceuticals, and biotechnology. Some red algae also play important roles in reef-building, particularly coralline algae, which deposit calcium carbonate in their cell walls. Reproduction in red algae can be asexual through fragmentation or spore formation, and sexual, involving specialized gametes and a unique process where the male gamete does not actively swim.