red algae

The red algae (or Rhodophyta, pronounced /roʊˈdɒfɨtə/, /ˌroʊdəˈfaɪtə/, from Greek: ῥόδον (rhodon) = rose + φυτόν (phyton) = plant, thus red plant) are one of the oldest groups of eukaryotic algae,[2] and also one of the largest, with about 5,000–6,000 species of mostly multicellular, marine algae, including many notable seaweeds. Other references indicate as many as 10,000 species;[4] more detailed counts indicate ~4000 in ~600 genera (3738 marine spp in 546 genera and 10 orders (plus the unclassifiable); 164 freshwater spp in 30 genera in 8 orders).

The red algae form a distinct group characterized by the following attributes: eukaryotic cells without flagella and centrioles, using floridean starch as food reserve, with phycobiliproteins as accessory pigments (giving them their red color), and with chloroplasts lacking external endoplasmic reticulum and containing unstacked thylakoids. Most red algae are also multicellular, macroscopic, marine, and have sexual reproduction.

Many of the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse (Palmaria palmata) and laver (nori/gim) are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans and other food additives.