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Overview

Brief Summary

If you ever try walking close to the waterline on a sea dike, you surely have noticed how slippery it can be. This slipperiness is caused by gutweed, a green seaweed. Green seaweed gets its bright green color from the dominating chlorophyll pigment. There are more than sixty species found in the Netherlands. All 'higher plants', from eelgrass to trees, find their origin in one-celled green algae. Just like red seaweed, green seaweeds degrade more rapidly than brown seaweeds. They make a good source of nutrients for annual seablite.
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The Chlorophyceae are one of the lineages of primarily freshwater green algae.

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Physical Description

Morphology

There are a variety of thallus types among the chlorophyceans.

  • Unicells:
    • Flagellated
      • individuals or
      • colonies
    • unflagellated except in reproductive state
    • with unflagellated asexual reproductive cells
  • Sarcinoid aggregations of nonmotile cells in which daughter cells fail to separate after division
  • Coenobium, a colony in which the number and arrangement of cells can be constant
  • Filaments:
    • unbranched or
    • branched
  • Multinucleate siphonous

(Graham & Wilcox, 2000)

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Diagnostic Description

  • Motile cells with radial or near-radial external symmetry
  • Flagella attached at the anterior end of the cell
  • The possibility of a rhizoplast
  • No multilayered structure
  • Eyespots common
  • Glycolate breaddown by glycolate dehydrogenase
  • Urea breakdown by urea amidolyase
  • Theca covering the cells (some of the flagellates have lost this characteristic)
  • Collapsing telophase spindle that brings daughter cells close together, followed by cell-division by a phycoplast*
  • Flagellar root system cruciate

*”type of cell division in which the mitotic spindle disperses after nuclear division with the two daughter nuclei coming close together, another set of microtubules arising perpendicular to the former position of the microtubules of the mitotic spindle, and the new cell wall forming along these microtubules.”

(Lee, 1999)

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Ecology

Habitat

Primarily freshwater or terrestrial (soils, tree bark, etc.) some in brackish or marine water (Graham & Wilcox, 2000).

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Life History and Behavior

Life Cycle

Meiosis occurs when the zygote germinates, so that most of the lifecycle is haploid (Lee, 1999).

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Reproduction

Those taxa for which the sexual reproductive process is known produce a dormant zygote, with meiosis usually occurring when the zygote germinates (Lee, 1999).

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Evolution and Systematics

Evolution

Systematics and Taxonomy

Under the old five kingdom system of classification, all the algae were placed within the Kingdom Protista. However, the molecular research of the last decades has resulted in major reclassifications, and at least for now, some uncertainty and disagreement. There is no debate about the placement of the algae in the Domain Eukarya – they have eukaryote cells. And, for the most part, there seems to be agreement that the green algae are members of the plant kingdom. However, classification into lower taxa is less clear.

For example, Lee (1999) defines Chlorophyceae as a taxon within the class(?) Chlorophyta and with the following orders:

  • Volvocales – can be unicellular or multicellular; the vegetative cells are flagellated & motile
  • Tetrasporales – non-filamentous colonies with immobile vegetative cells capable of cell division; pseudocilia may be present
  • Schizogoniales – foliose marine algae with stellate choroplasts
  • Chlorococcales – unicellular or non-filamentous colonial algae; if colonial, daughter colonies formed as coenobia; vegetative cells non-motile
  • Sphaerophleales – unbranched filaments with new walls formed inside the old filament walls, resulting in H-shaped wall pieces
  • Chlorosarcinales – daughter cells retained within parent cell wall; no plasmodesmata present
  • Chaetophorales – branched or unbranched filaments; plasmodesmata present
  • Oedogoniales – uninucleate filamentous freshwater algae with a unique type of cell division; motile spores and gametes with a whorl of flagella at one pole

In Graham and Wilcox (2000), the Chlorophyceans are a lineage of green algae, encompassing the following clades:

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:875Public Records:843
Specimens with Sequences:849Public Species:413
Specimens with Barcodes:830Public BINs:0
Species:418         
Species With Barcodes:408         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Chlorophyceae

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Relevance to Humans and Ecosystems

Benefits

Uses

Chlamydomonas and Volvox are important laboratory model systems, Selensastrum capricornutum is widely recognized for its utility as a bioassay organism, and Dunaliella and Botryococcus can be valuable in production of industrially useful materials.” (Graham & Wilcox, 2000)

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