Red algae

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Red algae
Temporal range: Mesoproterozoic–present[1]
Scientific classification
Domain: Eukarya
(unranked): Archaeplastida
Division: Rhodophyta
Wettstein, 1922

Classification is currently disputed. See Taxonomy.

The red algae, or Rhodophyta (/rˈdɒftə/ roh-DOF-fit-tə or /ˌrdəˈftə/ ROH-də-FY-tə; from Ancient Greek: ῥόδον rhodon, "rose" and φυτόν phyton, "plant"), are one of the oldest groups of eukaryotic algae,[2] and also one of the largest, with about 5,000–6,000 species[3] of mostly multicellular, marine algae, including many notable seaweeds. Other references indicate as many as 10,000 species;[4] more detailed counts indicate about 4,000 in about 600 genera (3,738 marine species in 546 genera in 10 orders, plus the unclassifiable; and 164 freshwater species in 30 genera in eight orders).[5]

The red algae form a distinct group characterized by having eukaryotic cells without flagella and centrioles, chloroplasts that lack external endoplasmic reticulum, contain unstacked thylakoids[4] and use phycobiliproteins as accessory pigments (giving them their red color). They store floridean starch, a type of starch that consists of highly-branched amylopectin without amylose,[6] as food reserves outside their plastids. Most red algae are also multicellular, macroscopic, marine, and use sexual reproduction to reproduce. They have alternation of generations and may have three generations rather than two.[7]




Fossil record[edit]

One of the oldest fossils 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 1.2 billion years ago.[1]


Calcite crusts, which have been interpreted as the remains of coralline red algae, date to the terminal Proterozoic.[10] Thallophytes resembling coralline red algae are known from the late Proterozoic Doushantuo formation.[11]


Further information: Wikispecies:Rhodophyta


The system reflected the consensus in 2005. Many studies published since then have provided evidence that is in agreement.[13][14][15][16] However, other studies have suggested Archaeplastida is paraphyletic.[17][18] As of January 2011, the situation appears unresolved.




Classification comparison[edit]

Classification system according to
Saunders and Hommersand 2004[19]
Classification system according to
Hwan Su Yoon et al. 2006[20]
Orders Multicelluar? Pit plugs? Example
Cyanidiales No No Cyanidioschyzon merolae
Rhodellales No No Rhodella
Compsopogonales, Rhodochaetales, Erythropeltidales Yes No Compsopogon
Rufusiales, Stylonematales Yes No Stylonema


Yes Yes Bangia, "Porphyra"


No No Porphyridium cruentum
Hildenbrandiales Yes Yes Hildenbrandia
Rhodogorgonales, Corallinales Yes Yes Corallina officinalis
Ahnfeltiales, Pihiellales Yes Yes Ahnfeltia


Species of red algae[edit]

Around 6,500 to 10,000 species are known,[4][8] nearly all of which are marine, with about 200 that live only in fresh water. However, estimates of the number of real species vary by 100%.[4]

Some examples of species and genera of red algae are:

Genomes of red algae[edit]

Complete genome sequences are only available for 5 species of red algae, including 4 published in 2013.

No genome sequences are available for members of the classes Compsopogonophyceae, Rhodellophyceae and Stylonematophyceae.

Relationship to Chromalveolata chloroplasts[edit]

Chromalveolatas seem to have evolved from Bikonts that have acquired red algae as endosymbionts. According to this theory, over time these Bikonts and their endosymbiont red algae have evolved to become Chromalveolata and their chloroplasts. This part of endosymbiotic theory is supported by various structural and genetic similarities.[28]


Algal group δ13C range[29]
HCO3-using red algae −22.5‰ to −9.6‰
CO2-using red algae −34.5‰ to −29.9‰
Brown algae −20.8‰ to −10.5‰
Green algae −20.3‰ to −8.8‰


Red algae are red due to phycoerythrin. They contain the sulfated polysaccharide carrageenan in the amorphous sections of their cell walls, although red algae from the genus Porphyra contain porphyran. They also produce a specific type of tannin called phlorotannins, but in lower amount than brown algae do.


Red algae have double cell walls.[30] The outer layers contain the polysaccharides agarose and agaropectin that can be extracted from the cell walls by boiling as agar.[30] The internal walls are mostly cellulose.[30]

Pit connections and pit plugs[edit]

Main article: Pit connection

Pit connections[edit]




Connections that exist between cells not sharing a common parent cell are labeled secondary pit connections. These connections are formed when an unequal cell division produced a nucleated daughter cell that then fuses to an adjacent cell. Patterns of secondary pit connections can be seen in the order Ceramiales.

Pit plugs[edit]












Life cycle[edit]


Carpospores may also germinate directly into thalloid gametophytes, or the carposporophytes may produce a tetraspore without going through a (free-living) tetrasporophyte phase.[31] Tetrasporangia may be arranged in a row (zonate), in a cross (cruciate), or in a tetrad.[2]



In a simple case, such as Rhodochorton investiens:





A rather different example is Porphyra gardneri:


Human consumption[edit]

Some red algae are iridescent when not covered with water

Several species are important food crops, in particular members of the genus Porphyra, variously known as nori (Japan), gim (Korea), or laver (Britain). Dulse (Palmaria palmata)[32] is another important British species.[33] These rhodophyte foods are high in vitamins and protein and are easily grown; for example, nori cultivation in Japan goes back more than three centuries.


See also[edit]


  6. ^ Viola, R.; Nyvall, P.; Pedersén, M. (2001). "The unique features of starch metabolism in red algae.". Proceedings of the Royal Society of London B 268: 1417=1422. doi:10.1098/rspb.2001.1644. 
  7. ^
  9. ^ Eloranta, P.; Kwandrans, J. (2004). "Indicator value of freshwater red algae in running waters for water quality assessment" (PDF). International Journal of Oceanography and Hydrobiology. XXXIII (1): 47–54. ISSN 1730-413X. 
  13. ^ Fabien Burki, Kamran Shalchian-Tabrizi, Marianne Minge, Åsmund Skjæveland, Sergey I. Nikolaev, Kjetill S. Jakobsen, Jan Pawlowski (2007). Butler, Geraldine, ed. "Phylogenomics Reshuffles the Eukaryotic Supergroups". PLoS ONE 2 (8): e790. doi:10.1371/journal.pone.0000790. PMC 1949142. PMID 17726520. 
  14. ^ Burki, Fabien; Inagaki, Yuji; Bråte, Jon; Archibald, John M.; Keeling, Patrick J.; Cavalier-Smith, Thomas; Sakaguchi, Miako; Hashimoto, Tetsuo; Horak, Ales; Kumar, Surendra; Klaveness, Dag; Jakobsen, Kjetill S.; Pawlowski, Jan; Shalchian-Tabrizi, Kamran (2009). "Large-Scale Phylogenomic Analyses Reveal That Two Enigmatic Protist Lineages, Telonemia and Centroheliozoa, Are Related to Photosynthetic Chromalveolates". Genome Biology and Evolution 1: 231–8. doi:10.1093/gbe/evp022. PMC 2817417. PMID 20333193. 
  17. ^ Kim, E.; Graham, L.E. & Graham, Linda E. (2008). Redfield, Rosemary Jeanne, ed. "EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata". PLoS ONE 3 (7): e2621. doi:10.1371/journal.pone.0002621. PMC 2440802. PMID 18612431 
  22. ^ Matsuzaki; et al. (April 2004). "(April 8, 2004) Genome sequence of the ultrasmall unicellular red alga Cyanidioschyzon merolae 10D". Nature 428 (6983): 653–7. doi:10.1038/nature02398. PMID 15071595. 
  23. ^ Nozaki et al. (July 10, 2007) A 100%-complete sequence reveals unusually simple genomic features in the hot-spring red alga Cyanidioschyzon merolae. BMC Biol. 2007; 5: 28. doi:10.1186/1741-7007-5-28
  24. ^ Schönknecht; et al. (Mar 2013). "(March 8, 2013) Gene Transfer from Bacteria and Archaea Facilitated Evolution of an Extremophilic Eukaryote". Science 339 (6124): 1207–1210. doi:10.1126/science.1231707. PMID 23471408. 
  25. ^ Nakamura; et al. "(March 11, 2013) The First Symbiont-Free Genome Sequence of Marine Red Alga, Susabi-nori (Pyropia yezoensis)". PLoS ONE 8 (3): e57122. doi:10.1371/journal.pone.0057122. 
  26. ^ Collen; et al. (2013). "Genome structure and metabolic features in the red seaweed Chondrus crispus shed light on evolution of the Archaeplastida". PNAS 110: 5247–5252. doi:10.1073/pnas.1221259110. 
  27. ^ Bhattacharya; et al. (2013). "Genome of the red alga Porphyridium purpureum". Nature Communications 4: 1941. doi:10.1038/ncomms2931. 
  28. ^ Summarised in Cavalier-Smith, Thomas (April 2000). "Membrane heredity and early chloroplast evolution". Trends in Plant Science 5 (4): 174–182. doi:10.1016/S1360-1385(00)01598-3. PMID 10740299. 

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