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(rōdŏf`ətə), phylum (division) of the kingdom ProtistaProtista
or Protoctista
, in the five-kingdom system of classification, a kingdom comprising a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms.
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 consisting of the photosynthetic organisms commonly known as red algaealgae
[plural of Lat. alga=seaweed], a large and diverse group of primarily aquatic plantlike organisms. These organisms were previously classified as a primitive subkingdom of the plant kingdom, the thallophytes (plants that lack true roots, stems, leaves, and flowers).
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. Most of the world's seaweedsseaweed,
name commonly used for the multicellular marine algae. Simpler forms, consisting of one cell (e.g., the diatom) or of a few cells, are not generally called seaweeds; these tiny plants help to make up plankton.
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 belong to this group. Members of the division have a characteristic clear red or purplish color imparted by accessory pigments called phycobilins, unique to the red algae and the cyanobacteriacyanobacteria
or blue-green algae,
photosynthetic bacteria that contain chlorophyll. For many years they were classified in the plant kingdom along with algae, but discoveries made possible by the electron microscope and new biochemical techniques have shown them to be
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. The chloroplasts of red algae are believed to be derived from cyanobacteria that formed an ancient symbiotic relationship with the algae.

Of the approximately 4,000 known species of red algae, nearly all are marine; a few species occur in freshwater. Although red algae are found in all oceans, they are most common in warm-temperate and tropical climates, where they may occur at greater depths than any other photosynthetic organisms. The red algae are multicellular and are characterized by a great deal of branching, but without differentiation into complex tissues. The red algal cell wall has a firm inner layer containing cellulose and a mucilaginous or gelatinous outer layer. Cells may have one or more nuclei, depending on the species. Cell division is by mitosismitosis
, process of nuclear division in a living cell by which the carriers of hereditary information, or the chromosomes, are exactly replicated and the two copies distributed to identical daughter nuclei.
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. The red algae are remarkable in that they are not flagellated; none has motile cells of any kind.

Cells of the Rhodophyta possess chloroplastschloroplast
, a complex, discrete green structure, or organelle, contained in the cytoplasm of plant cells. Chloroplasts are reponsible for the green color of almost all plants and are lacking only in plants that do not make their own food, such as fungi and nongreen parasitic
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 that, in addition to the phycobilins, contain chlorophyll a, carotenes, and xanthophylls. At great ocean depths, where the wavelength of light available for photosynthesis is very different from that in shallow water, the phycobilins become more active than the chlorophylls in absorbing light; this fact may explain the ability of red algae to exist at depths of up to 879 ft (268 m). The carbohydrate reserves of red algae are in the form of floridean starch, a specialized glucose polymer of different structure than the starch of plants.

The life cycle of the red algae is extremely complex, involving one haploid phase and two diploid phases. Most marine red algae have soft and delicate bodies, or thalli; however, the coralline algae have thalli that become strongly calcified and contribute significantly to the growth of coral reefs in tropical seas. Because of the permanent nature of the structures that they produce, coralline algae have a rich fossil record that extends back as far as 700 million years. Commercial agaragar
, product obtained from several species of red algae, or seaweed, chiefly from the Ceylon, or Jaffna, moss (Gracilaria lichenoides) and species of Gelidium, harvested in eastern Asia and California.
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, used as a culture medium for bacteria and other organisms as well as for other purposes, is produced from several genera of red algae. The so-called Irish moss is the source of carrageenin, a substance widely used as a stabilizing agent in emulsions and in ice cream.


See H. C. Bold and M. J. Wynne, Introduction to the Algae: Structure and Reproduction (1985); C. A. Lembi and J. R. Waaland, Algae and Human Affairs (1988); C. van den Hoek, Algae: an Introduction to Phycology (1994).



a division of algae; red algae.

The red algae include unicellular and multicellular forms. All are characterized by the presence in the chromatophores (in addition to chlorophyll a, carotene, and xanthophyll) of chlorophyll d, R-phycoerythrin (a red pigment), and R-phycocyan (a blue-green pigment); by the absence of motile flagellate stages (zoospores and spermatozoa); and by a unique sexual process. The thalli are filamentous, bushy, or lamellar; in some, they are divided into stems and leaflike organs. In a number of species, the thalli are hardened because of calcium deposits (Lithothamnion). The color of the red algae varies from dark red (almost black) to pink, yellowish, and, (occasionally) steel blue. Reserve nutrients include red-algal starch, floridoside, and mannoglycer-ate.

The division Rhodophyta comprises 600 genera (3,750 species). It is divided into two classes: Bangiophyceae and Florido-phyceae. Asexual reproduction proceeds by means of nonmotile spores, which form in sporangia singly (monospores) or in groups of four (tetraspores). Sexual reproduction proceeds by the process of oogamy. Nonmotile gametes, called spermatia, form in the male sex organs, or spermatangia. The spermatia are carried in the water to the female sex organs, or carpogonia. After fertilization, the contents of the carpogonium, in the Bangiophyceae, break up into haploid carpospores; in the Floridophyceae, the carpogonium yields filamentous multicellular processes, on each end of which forms a carpospore. Alternatively, threads emerge from the carpogonium that join together with special large (auxiliary) cells of the thallus, to which are transferred the nuclei that form during the division of the fertilized egg of the carpogonium (one to each). The nuclei within the auxiliary cells do not merge; these cells, in turn, yield filamentous processes bearing carpospores.

Rhodophyta are predominantly marine, often flourishing at greater depths than green and brown algae, owing to the presence of phycoerythrin, which is apparently capable of utilizing green and blue light rays (which penetrate deeper in water than others) for photosynthesis. Less often, the red algae are found in fresh waters and soil. Fossil Rhodophyta have been found in Cretaceous deposits. Ahnfeltia, Gelidium, Phyllophora, and Fur-cellaria are of the greatest practical value, yielding jelling substances (agar, agaroid, and carrageenin). Some members of the group, such as Porphyra, are used as food.


Kursanov, L. I. Burye i krasnye vodorosli. Moscow, 1927.
Zinova, E. S. “Vodorosli Iaponskogo moria: Krasnye vodorosli (Rhodophyceae).” Trudy Tikhookeanskogo komiteta, 1940, vol. 5.
Zinova, A. D. Opredelitel’ krasnykh vodoroslei severnykh morei SSSR. Moscow-Leningrad, 1955.
Kylin, H. Die Gattungen der Rhodophyceen. Lund, 1956.



The red algae, a large diverse phylum or division of plants distinguished by having an abundance of the pigment phycoerythrin.
References in periodicals archive ?
The lowest level of the intertidal level, together with the sublittoral includes populations of rhodophytes, such as Laurencia, Lomentaria articulata, Plumaria elegans (found more to the north), Pterosiphonia complanata (more to the south), Membranoptera alata, Mastocarpus stellatus, and Palmaria palmata.
These adventurers include rhodophytes, such as Laurencia pinnatifida and L.
Rhodophytes such as Hildenbrandia are very common, together with other algae encrusted on the rocks and masses of cyanobacteria that fix atmospheric nitrogen.
There are also some rhodophytes such as Gigartina papillata and Porphyra laminaris, and some fucaceans, including some clear examples of vicariance; the niche of the European species Pelvetia canaliculata, for example, is occupied by Pelvetiopsis limitata.
Green algae (chlorophytes), brown algae (phaeophytes), and red algae (rhodophytes) cover submerged rocks all over the world, wherever there is a little light for photosynthesis.
These include the chlorophyte (Ulva rigida and Bryopsis muscosa), the rhodophyte (Scottera nicaeensis, Plocamium cartilagineum [=P.
286 Roadside drying of rhodophytes on the island of Terceira (Azores).
Dulse is elaborated from the rhodophyte Palmaria palmata and has been consumed since Viking times in Scotland, Ireland, and Iceland, although the most important current market is in the maritime provinces of Canada, mainly Nova Scotia.
Thus, a polyclonal antibody raised to a rhodophyte LHCI should have a good chance of specifically recognizing the LHCI polypeptides in V.
Molecular biology of rhodophyte and chromophyte plastids.