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Red algae

(Redirected from Rhodophyta)

iRed algae
Red algae:Laurencia
Scientific classification
Kingdom: Protista
Phylum: Rhodophyta
Wettstein, 1922
Possible classes

The red algae (Rhodophyta, IPA: [ˌrəʊdə(ʊ)ˈfʌɪtə], from Greek: ῥόδον (rhodon) = rose + φυτόν (phyton) = plant, thus red plant) are a large group of mostly multicellular, marine algae, including many notable seaweeds. Most of the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse and nori are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans and other food additives.


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Biology

Many red algae have multicellular stages but these lack differentiated tissues and organs. Unlike most other algae, no cells with a flagellum are found in any member of the group. Unicellular forms typically live attached to surfaces rather than floating among the plankton, and both the larger female and smaller male gametes are non-motile, so that most have a low chance of fertilization. They have cell walls that are made out of cellulose and thick gelatinous polysaccharides which are the basis for most of the industrial products made from red algae.

Red algae:"Florideae" from Ernst Haeckel's Artforms of Nature, 1904
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"Florideae" from Ernst Haeckel's Artforms of Nature, 1904

The chloroplasts of red algae are bound by a double membrane, like those of green plants; both groups (Archaeplastida) probably share a common origin. Their plastids formed by direct endosymbiosis of a cyanobacteria, and in red algae are pigmented with chlorophyll a and various proteins called phycobiliproteins, which are responsible for their reddish color. Other reddish algae are classified not as red algae but as Chromista which are hypothesied to have acquired their chloroplasts from red algae through endosymbiosis.

Fossil record

The oldest fossil identified as a red alga is also the oldest fossil eukaryote that belongs to a specific modern taxon. Bangiomorpha pubescens, a multicellular fossil from arctic Canada, strongly resembles the modern red alga Bangia despite occurring in rocks dating to 1200 million years ago.[1]

Red algae are important builders of limestone reefs. The earliest such coralline algae, the solenopores, are known from the Cambrian Period. Other algae of different origins filled a similar role in the late Paleozoic, and in more recent reefs.

Taxonomy

The diverse eukaryotes that constitute the red algae have been the focus of numerous recent molecular surveys and remain a rich source of undescribed and little known species for the traditional taxonomist. Molecular studies place the red algae in the Archaeplastida (Plantae sensu lato); however, supraordinal classification has been largely confined to debate on subclass vs. class level status for the two recognized subgroups, one of which is widely acknowledged as paraphyletic. This narrow focus has generally masked the extent to which red algal classification needs modification.

Below are two valid published taxonomies of the red algae, although neither necessarily has to be used, as the taxonomy of the algae is still in a state of flux. Note also that there is continued scientific debate as to whether the Rhodophyta should be included in the Kingdom Protista or the Kingdom Plantae. These two classification systems, which place the red algae in the plant kingdom, are shown in the table below.

Classification system according to
Hwan Su Yoon et al. 2006[2]		Classification system according to
Saunders and Hommersand 2004[3]
Kingdom Plantae Haeckel
  • Subkingdom Biliphyta Wettstein
    • Phylum Rhodophyta Wettstein
      • Subphylum Cyanidiophytina subphylum novus
        • Class Cyanidiophyceae Merola et al
      • Subphylum Rhodophytina subphylum novus
        • Class Bangiophyceae Wettstein
        • Class Compsopogonophyceae Saunders et Hommersand
        • Class Florideophyceae Cronquist
        • Class Porphyridiophyceae classis nova
        • Class Rhodellophyceae Cavalier-Smith
        • Class Stylonematophyceae classis nova
Kingdom Plantae Haeckel
  • Subkingdom Rhodoplantae
    • Phylum Cyanidiophyta
      • Class Cyanidiophyceae Merola et al
    • Phylum Rhodophyta Wettstein
      • Subphylum Rhodellophytina
        • Class Rhodellophyceae Cavalier-Smith
      • Subphylum Metarhodophytina
        • Class Compsopogonophyceae Saunders et Hommersand
      • Subphylum Eurhodophytina
        • Class Bangiophyceae Wettstein
        • Class Florideophyceae Cronquist
          • Subclass Hildenbrandiophycidae
          • Subclass Nemaliophycidae
          • Subclass Ahnfeltiophycidae
          • Subclass Rhodymeniophycidae

Species

There are around 4,100 known species, with nearly all of them marine, and only 200 that live in freshwater. Some examples are:

Red Algae as food

Several species are used as food. Dulse (Palmaria palmata) and Porphyra are perhaps the best known[4].

See also

References

Butterfield, Nicholas J. 2000. Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes. Paleobiology 26 (3): 386–404.

  1. ^ Butterfield, Nicholas J. 2000. Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes. Paleobiology 26 (3): 386–404.
  2. ^ Yoon, Hwan Su, K. M. Müller, R. G. Sheath, F. D. Ott, and D. Bhattacharya. (2006). Defining the major lineages of red algae (Rhodophyta). J. Phycol. 42:482-492
  3. ^ Saunders, Gary W., Hommersand, Max H. (2004). Assessing red algal supraordinal diversity and taxonomy in the context of contemporary systematic data. Am. J. Bot. 91: 1494-1507
  4. ^ Mumford, T.F. and Muira, A. Porphyra as food: cultivation and economics. in: Algae and Human Affairs. edited: Lembi, C.A. and Waaland, J. 1988. Cambridge University Press, Cambridge

Categories


Protista | Algae | Red algae

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