Algae: Protists with Chloroplasts

David J. Patterson

The algae are a polyphyletic and paraphyletic group of organisms. They are defined in differing ways, but are usually considered to be the photosynthetic organisms excepting plants. Using the term 'plants' in its most restrictive fashion, the algae are then photosynthetic organisms excepting the sister group to the Charales (i.e. the land plants). Such a definition allows inclusion of photosynthetic prokaryotes such as the cyanobacteria. The definition applied here is that the algae is that artificial subset of the photosynthetic eukaryotes which excludes the sister group to the Charales (land plants).

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 Euglena oxyuris (Euglenida), a unicellular alga

Left: Dicroglossum crispatulum, a multicellular red alga (Rhodophyta).
Copyright 2000 Alan Millar, Royal Botanic Gardens, Sydney, Australia
Right: Euglena oxyuris (Euglenida), a unicellular alga.
Copyright 2000 David J. Patterson

The algae are the dominating primary producers in aquatic ecosystems, on unstable substrates (muds and sands) and in intertidal marine habitats. Algae are commonly exploited as foodstuffs, food additives, toothpastes, etc.

The ability for eukaryotes to carry out photosynthesis was made possible by one or more symbiotic associations between heterotrophic eukaryotes and photosynthetic prokaryotes (or their descendents). There were several primary symbioses between eukaryotes and blue green algae. In one lineage, the photosynthetic organism lost much of its genetic independence and became functionally and genetically integrated as chloroplasts within the host cell. Modern chloroplasts, also called plastids, are bounded by two or more membranes, and most usually lie free in the cytoplasm, but in some cases they may be located within a fold of the nuclear envelope, or may be associated with the cytoplasm and residual nucleus of a eukaryotic endosybiont. The descendents of some of these primary plastids have gone on to form further associations. At least two types of protists (chloroarachniophytes and cryptomonads) have acquired 'plastids' by forming symbioses with eukaryotic algae. This are referred to as secondary symbioses.

Algae are distinguished on a number of different characteristics. The most important ones are:

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a species of Euglena (Euglenozoa, Euglenida) with its colour arising from chlorophyll b in the plastids

Left: a species of Euglena (Euglenozoa, Euglenida) with its colour arising from chlorophyll b in the plastids.
Right: Gymnodinium (alveolate, dinoflagellate) with plastids containing chlorophylls a and c and consequently brown in colour.
Photographs copyright 2000 David J. Patterson

Algal protists occur in 8 lineages. These are summarised below.

Groups of Algae

ALVEOLATES Contains some algae, autotrophic dinoflagellates, diverse, Peridinium, Symbiodinium, Ceratium unicellular, colonial, syncytial; free-living, symbiotic and parasitic chlorophylls a and c, some symbionts
CHLORARACHNIOPHYTES A few genera of amoeboid organisms all with symbiotic algae, Chlorarachnion syncytial, free-living Chlorophyll b
CRYPTOMONADS About 12 genera of flagellates, Cryptomonas single cells, rarely forming colonies, some are endobiotic Chlorophylls a and c, phycobilins
EUGLENIDS about half of the genera (35) contain members with green chloroplasts, flagellates, Euglena, Trachelomonas single cells Chlorophyll b
GLAUCOPHYTES Several genera of flagellated and non-flagellated protists with similar phycobilin-rich symbionts, e.g. Glaucocystis, Cyanophora flagellated and non-flagellated cells Phycobilin
HAPTOPHYTES Diverse, with many genera, all or all bar one genera with plastids, with naked species and those with scales (coccolithophores) single cells, some are endosymbionts Chlorophylls a and c
RED ALGAE (Rhodophyta) All species are regarded as algal free-living and parasitic, single celled, and multicellular Phycobilins
STRAMENOPILES Most but not all stramenopiles are algae, the group includes diatoms, brown algae, synurophytes and other 'chrysophytes' single celled, colonial and multicellular, free-living and parasitic Chlorophylls a and c
VIRIDAEPLANTAE The green algae, all but a few genera are algal, prasinophytes, chlorophyta (e.g. volvocalean algae, conjugatopohytes, Ulvales, Charales) single celled, colonial and multicellular, free-living Chlorophyll b

Genera of algal protists for which no clear ultrastructural identity has been developed (after Patterson, 1999):

  • Adinomonas
  • Archaeosphaerodiniopsis
  • Aurospora
  • Berghiella
  • Bjornbergiella
  • Boekelovia
  • Camptoptyche
  • Chalarodora
  • Chlamydomyxa
  • Copromonas
  • Cyanomastix
  • Dinoasteromonas
  • Dinoceras
  • Glaucocystopsis
  • Goniodinium
  • Heteromastix
  • Hillea
  • Histiophysis
  • Isoselmis
  • Melanodinium
  • Meringosphaera
  • Monodus
  • Nephrodinium
  • Pachydinium
  • Peliainia
  • Petasaria
  • Phialonema
  • Pleuromastix
  • Pseudoactiniscus
  • Strobilomonas
  • Syncrypta
  • Tetragonidium
  • Thaulirens
  • Thaumatodinium
  • Thylakomonas
  • Triangulomonas
About This Page

David J. Patterson
Marine Biological Laboratory, Woods Hole, Massachusetts, USA

Page: Tree of Life Algae: Protists with Chloroplasts Authored by David J. Patterson. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

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