Domain Eukaryota
Rhodophyta - Red Algae
Porphyra species

The Rhodophyta or Red Algae are a large and diverse group of mulitcellular marine algae.

Many are notable and beautiful algae. The 4,000+ species continue to elude classification.


The Rhodophyta, like other Archaeplasdida, all have photosynthesizing chloroplasts wrapped in double membranes (inherited from an anciently absorbed cyanobacteria). They have chlorophyll a, but unlike Land Plants, lack b. They have the piment phycobilin, which give the Rhodophyta their reddish color (and allows them to absorb light at greater water depths).
Most Rhodophyta have multicellular forms but lack cellular differentiation - the 'division of labor' into tissues and organs. Instead they have a thallus, a body without true roots, stems or leaves. Polysiphonia species


Most are immobile, attached to surfaces or to other algae. Unlike other algae, the Red Algae have no flagella at any point.

They have a complex three-part life cycle using cellular division, eggs and sperm, and/or spores. Their reproductive cells (gametes) can't move, but they manage to proliferate nonetheless.

Like the Land Plants, the Rhodophyta have cellulose in their cell walls. They also have stcky polysaccharide starches, which make them economically valuable as thickening agents for many foods and industrial products.
Microcladia coulteri The Rhodophyta take many forms - tiny and delicate; spreading filaments, wavy sheets; large and 'fleshy', or covered in coral-like carbonate shells. Classification schemes face regular modification and many species remain undescribed.


Genetic studies continue. The following are currently tentative groups:

  • The Florideophytes are a large, widespread group. They grow only from the tips of the branching thallus. The simple chloroplasts are disc-shaped.
  • The Bangiales have thalli with soft, thin filaments spreading in dense layers.
  • The Porphyridiales are widespread and grow in papery-thin sheets along shorelines. They have a slippery texture and resists dryness well. Often used for food (nori, kim)
  • The Compsopogonales have branching filaments and found in freshwater streams. Possibly related to:
  • The Batrachospermum, with tangled, beaded; gelatinous filaments. Found in freshwater streams.
  • The Cyanidiophytes are blue-green, unicellular and form aggragated mats. Branched off early from kingdom.
  • The Rhodellophyceae are single-celled and like brackish waters..
  • The Corallinales are coral-like. They have a dense thallus and form a calcium carbonate skeleton.
  • The Gigartinales have large thalli and fleshy, brownish-red fronds. Source of carageenan, a common food additive.

 
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