Red algae
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The red algae (Rhodophyta, pronounced /ˈrəʊdə(ʊ)ˌfʌɪtə/, ancient Greek: rhodos phytos = 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 certain other products like agar and food additives.
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 are made out of cellulose and thick gelatinous polysaccharides, which are the basis for most of the industrial products made from red algae.
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 phycobilins, which are responsible for their reddish color. Other algae that lack chlorophyll b appear to have acquired their chloroplasts from red algae, although their pigmentations are somewhat different.
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.
The most current classification system is below (Saunders et. al., 2004). Note that while this is a valid published taxonomy it does not necessarily have to be used as the taxonomy of the algae is still in a state of flux.
Kingdom Protist
- Subkingdom Rhodoplantae
- * Phylum Cyanidiophyta
- ** Class Cyanidiophyceae
- * Phylum Rhodophyta
- ** Subphylum Rhodellophytina
- *** Class Rhodellophyceae
- ** Subphylum Metarhodophytina
- *** Class Compsopogonophyceae
- ** Subphylum Eurhodophytina
- *** Class Bangiophyceae
- *** Class Florideophyceae
- **** Subclass Hildenbrandiophycidae
- **** Subclass Nemaliophycidae
- **** Subclass Ahnfeltiophycidae
- **** Subclass Rhodymeniophycidae
Examples
Lemanea; Palmaria palmata.References
- 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,
See also
- Brown algae
- Green algae
- Red tide (Red tides are caused by algae from the phylum Dinoflagellata, and not Red Algae [Rhodophyta])
- Françoise Ardré (namesake of the red alga known as Pterosiphonia ardreana)
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