Green Algae

Abstract

The green algae are a large and diverse group of photosynthetic eukaryotes. They comprise many ancient and diverse lineages, including land plants. Through evolutionary time, green algae have formed a number of symbiotic associations with fungi and animals and their chloroplasts have been incorporated into other eukaryotic organisms through secondary endosymbioses. Green algae display many degrees of organismal complexity: from microscopic unicells to macroscopic, multicellular thalli more than a metre in length. They are critical components of almost all aquatic ecosystems and many terrestrial ecosystems as well. Green algae are commercially important as feed and as a source of many industrial and pharmaceutical chemicals. Available chloroplast, mitochondrial and nuclear genomic data have contributed greatly to our understanding of their biology and evolutionary history. Scientists are still discovering new species and lineages of green algae as well as novel biological and chemical characteristics.

Key Concepts:

  • Green algae are extraordinarily diverse morphologically and are separated taxonomically into two phyla, Chlorophyta and Charophyta.

  • Embryophyte land plants evolved from green algae in Charophyta.

  • Similar morphological forms of vegetative cells evolved in independent lineages of green algae.

  • As primary producers, green algae are important components of marine, freshwater and terrestrial ecosystems.

  • Green algae are important model organisms.

  • Green algae are important symbionts with fungi, bacteria, animals and plants.

  • Green algae are economically important as sources of industrial products, biofuels and food.

  • Most groups of green algae are poorly studied and many new species are being discovered.

Keywords: biofuels; Chlorophyta; Charophyta; endosymbiosis; genomics; phylogeny; symbiosis

Figure 1.

Sampling of vegetative morphology seen in different member of the green algae: (a) Haematococcus, Chlorophyceae, microscopic; (b) Cosmarium, Zygnemophyceae, microscopic; (c) Acetabularia, Ulvophyceae, macroscopic; (d) Ulva, Ulvophyceae, macroscopic; (e) Draparnaldia, Chlorophyceae, microscopic; (f) Scenedesmus, Chlorophyceae, microscopic; (g) Eremosphaera, Trebouxiophyceae, microscopic; (h) Udotea, Ulvophyceae, macroscopic.

Figure 2.

Diagrammatic summary of the phylogenetic relationships of major groups of green algae (plus embryophytes).

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Lewis, Louise A, Hall, John D, and Zechman, Frederick W(Nov 2011) Green Algae. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000333.pub2]