I. SYNONYMS: Green algae, chlorophytes, chlorophyceans.

II. NUMBER: >8,000 species

III. PHYLUM CHARACTERISTICS:

• A. Structure and Physiology
  • Cell Form: Unicells, coenobia (text with tooltip) A coenobium (coenobia) is a type of colony in which the number of cells is predetermined. So, after formation, the cells of the colony cannot continue to divide to add to it. , filaments, parenchymatous (text with tooltip) Parenchymatous (adj.) refers to the formation of a multicellular organism or structure by cells that can divide in multiple planes and thus produce a mass of cells. , siphonous (text with tooltip) Siphonous (adj) describes a filament that has no cross walls. , colonies.
  • Flagella: Two flagella (or in pairs), both whiplash or with sparse hairs or scales and anteriorly directed (text with tooltip) An anteriorly-directed flagellum extends in the direction of the motion of the motile cell. The interpretation is that the flagellum functions by pulling the cell. .
  • Basal Bodies: Basal bodies opposite (text with tooltip) Basal bodies (also called kinetosomes) are organelles that are not membrane-bound. All eukaryotic flagella (also called undulipodia) are underlain or attached to the cell by the basal body. The basal body is a microtubular structure with the general formula 9(3)+0. They are indistinguishable from centrioles. , clockwise or counterclockwise in orientation with cruciate flagellar (text with tooltip) In the form of a cross. roots.
  • Cell Covering: Usually a wall of cellulose.
  • Chloroplasts: Variable; grass green with chlorophylls a and b, B-carotene and various xanthophylls. Eyespot (text with tooltip) An eyespot is a light-sensitive structure that does not form an image. This can be part of an organelle as in the chloroplast of certain microbial eukaryotes. It can be an elaborate structure that involves a light-sensitive swelling at the base of a flagellum (as in the euglenoids) or it can be a multicellular structure as in planarians. , when present, is always enclosed within the chloroplast.
  • Food Reserves: True starch that is deposited within the chloroplast in association with a pyrenoid.
  • Mitochondria: Plate-like cristae (text with tooltip) Flat cristae (crista, sing.) are wall-like cristae within certain mitochondria. .
  • Golgi: Present.
  • Nucleus: Usually haploid in vegetative forms however this varies. The siphonaceous greens are often diploid in the vegetative state.
  • Centrioles: Centrioles in some. Centrioles polar (text with tooltip) Polar centrioles occur at the poles of the nucleus, often one with polar fenestrae (polar openings). in Chlorophyceae and Ulvaphyceae. Metacentric (text with tooltip) Metacentric centrioles are unusual in that they form near the metaphase plate of certain green algae. in Trebuxiophyceae.
  • Inclusions and Ejectile Organelles: Not present.

• B. Mitosis, Meiosis and Life History
  • Mitosis: Variable, mostly closed (text with tooltip) Mitosis is closed when the segregation of daughter chromosomes occurs within the bounds of the nuclear membrane (the nuclear membrane does not break down). ; usually persistent telophase spindle a phycoplast (text with tooltip) A phycoplast is a microtubular array that follows mitosis and is oriented perpendicularly to the axis of the spindle. It serves to keep the daughter nuclei separated during cytokinesis. The phycoplast also serves as the organizing region in which furrowing and cell wall formation occurs after mitosis. Contrast this with a phragmoplast. . Cytokinesis by furrowing (text with tooltip) Furrowing is the means of cytokinesis in which the cell membrane pinches in from the outside to the center. Note that this is the opposite of cell plate formation in phragmoplastic plants. to cell plate (text with tooltip) A cell plate is the type of cell wall formation that occurs in a centrifugal fashion. This occurs in some green algae, all embryophytes, and some of the brown algae. formation.
  • Meiosis: Present.
  • Sexual Reproduction and Life History:
  • Varied; isogamy, anisogamy to oogamy. Oogamy seems to have evolved more than once in this phylum.
  • Life Histories of:
    • Hydrodictyon haplontic, isogamous, daughter colonies (autocolonies)
    • Volvox haplontic, oogamous, daughter colonies (coenobia)
    • Chlamydomonas haplontic, isogamy to oogamy, zoospores.
    • Oedogonium haplontic, oogamy, zoospores, fragmentation
    • Ulva isomorphic alternation of generation, isogamy, zoospores
    • Cladophora haplontic (at least one species has isomorphic alternation of generation), isogamy, zoospores, fragmentation
    • Codium diplontic, anisogamy
    • Acetabularia modified heteromorphic alternation of generation, isogamy

• C. Ecology: Freshwater, brackish water, marine environments, soil, parasites, phycobionts of fungi.