The Rhodophyta (red algae) are a distinct eukaryotic lineage characterized by the accessory photosynthetic pigments phycoerythrin, phycocyanin and allophycocyanins arranged in phycobilisomes, and the absence of flagella and centrioles (Woelkerling 1990). This is a large assemblage of between 2500 and 6000 species in about 670 largely marine genera (Woelkerling 1990) that predominate along the coastal and continental shelf areas of tropical, temperate and cold-water regions (Lüning 1990). Red algae are ecologically significant as primary producers, providers of structural habitat for other marine organisms, and their important role in the primary establishment and maintenance of coral reefs. Some red algae are economically important as providers of food and gels. For this reason, extensive farming and natural harvest of red algae occurs in numerous areas of the world.
Figure 1. Seaweed farmers tending a Kappaphycus line culture in the Philippines.
Kappaphycus and other Gigartinales species are grown commercially for the extraction of carrageenan, a gel used in many food products.
Image copyright © 2000, D. F. Kapraun.
Red algae have a number of general characteristics that in combination distinguish them from other eukaryotic groups:
- absence of flagella and centrioles
- floridean starch as a storage product and the storage of starch in the cytoplasm (Figure 2)
- phycoerythrin, phycocyanin, and allophycocyanin as accessory pigments
- unstacked thylakoids in plastids (Figure 3)
- no chloroplast endoplasmic reticulum
Figure 2. Griffithsia pacifica (Florideophyceae). Electron micrograph showing cytoplasm with numerous chloroplasts (C) and starch (S). Starch is the photosynthetic reserve and is deposited free in the cytoplasm.
Image copyright © 2000, C. M. Pueschel.
Figure 3. Griffithsia pacifica (Florideophyceae). Close-up of figure 2 electron micrograph showing a chloroplast with unstacked photosynthetic lamellae (arrows) bearing granules, called phycobilosomes (arrowheads), composed of water-soluble phycobiliprotein accessory pigments.
Image copyright © 2000, C. M. Pueschel.
Description of Rhodophyta
Description of Algae
Orthoclad Blue Black
Based on studies in:
New Zealand: Otago, Broad, Lee catchment (River)
New Zealand: Otago, Stony, Sutton catchment (River)
New Zealand: Otago, Dempster's Stream, Taieri River, 3 O'Clock catchment (River)
New Zealand: Otago, Sutton Stream, Taieri River, Sutton catchment (River)
This list may not be complete but is based on published studies.
- Townsend, CR, Thompson, RM, McIntosh, AR, Kilroy, C, Edwards, ED, Scarsbrook, MR. 1998. Disturbance, resource supply and food-web architecture in streams. Ecology Letters 1:200-209.
- Thompson, RM and Townsend, CR. 1999. The effect of seasonal variation on the community structure and food-web attributes of two streams: implications for food-web science. Oikos 87: 75-88.
Evolution and Systematics
Discussion of Phylogenetic Relationships
Taxa indicated by '*' are members of the traditional Bangiophyceae/Bangiophycidae that is now considered to be paraphyletic.
Traditionally the red algae were divided into two Classes the Bangiophyceae and Florideophyceae. Alternatively a single Class, the Rhodophyceae and two Subclasses, Bangiophycidae and Florideophycidae are used. Based on ultrastructure and molecular evidence the Bangiophyceae is now accepted as a paraphyletic group, while the Florideophyceae is considered to be monophyletic based on two synapomorphic characters - presence of a filamentous gonimoblast and tetrasporangia (Garbary & Gabrielson 1990 [and references within], Ragan et al. 1994).
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimen Records: 39358
Specimens with Sequences: 32199
Specimens with Barcodes: 21433
Species With Barcodes: 4116
Public Records: 21009
Public Species: 2188
Public BINs: 2647
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