I. Distribution
    FW, SW, many moist non-aquatic habitats, including snow banks, epiphytic epizoic forms. Larger non-filamentous forms usually marine. Aquatic forms usually filamentous, or unicellular, free floating or attached. Chlamydomonas - often on high altitude snow banks where it is the commonest cause of red snow. Certain green algae contribute to lichen formation.

II. Structure

A. General morphology.
    Unicellular, colonial or multicellular.
    Multicellular may be filamentous, may form thin leaf-like thalli, or may take on other shapes. There may be some tissue differentiation, but not to the point of complex tissues of vascular plants. Colonial flagellates may assume a disc like form, or that of a hollow sphere. Certain filamentous forms have lost some or all of their cross walls, thus forming a multinuclear protoplast - coenocytic plants.

B. Cell wall
    Usually two layers - inner firm, mainly cellulose, outer more gelatinous-often with pectin. Some unicellular flagellates lack true cell wall, but have a lorica wall-like structure which usually does not completely enclose the cell and which is not completely in contact with the protoplast, there being a space filled with water or gelatinous matrix. Lorica are often impregnated with minerals such as iron or calcium.

C. Nucleus
    Chlorophyta have a typical nucleus with chromosomes, nuclear membrane, nuclear sap, nucleoli, etc. and cell division is usually mitotic.

D. Chloroplasts and Food reserves
    Chlorophyll a and b and associated pigments present in definite chloroplasts. Chloroplasts vary in shape and number but are usually Consistent within a given species. No pigments other than the chlorophylls, and typical xanthophylls and Carotenes are found in the division. In many algae, the chloroplast contains one or more protein bodies known as pyrenoids. These are centers of starch accumulation. Some larger algae lack pyrenoids and accumulate starches in leucoplasts instead.

E. Flagellae
    All Contain the 9 + 2 pattern. At the base of a flagellum is a blepharoplast - a structure analogous to a Centriole. Most flagellae are of the whiplash type. Some have lateral filaments (mastigonemes),  these being the tinsel type. Those with one row of filaments are termed pectinate, those with 2 rows are pinnate.
    Usually 2 or 4 flagellae present on Chlorophytes, though 1-many are known. Flagellated Chlorophytes often have an orange red eyespot which influences the direction of travel of the organism.

A. Spores
    Commonest form is zoospore - motile, flagellated cell. Entire protoplast of a cell may form a single zoospore, mitosis may divide the protoplast into as many as 32 zoospores. Zoospores exit from the sporangium and are motile for a time - varying from minutes to days. Following this, it loses its flagellae, settles down, forms a cell wall, and becomes a vegetative cell. In addition to forming in sporangia, zoospores may be formed by meiosis in a zygote, or by mitosis from a akinete. Most zoospores are similar in appearance to the alga Chlamydomonas. Akinetes are sometimes formed and may grow directly into a new filament, or may divide into a number of zoospores. Yet another type of spore is the aplanospore similar to sporangiospores of cyanophytes. They differ from zoospores on having no flagella, having a cell wall

B. Sexual cycle
Involves alternating n and 2n stages.

1. Haplobiontic

a. Haplobiontic, adult haploid. Zygotic meiosis.
In the simplest pattern, the plant is n, producing n gametes by mitosis. These fuse to form a diploid zygote, which then undergoes meiosis to form 4 spores.

b. Haplobiontic, adult diploid. Gametic meiosis.

2. Diplobiontic.
A more complex pattern has the zygote undergoing mitosis, so that both an n and a 2n thallus is formed.

C. Terms for thalli:

1. Appearance
    a. If diploid and haploid thalli are alike - isomorphic
    b. If diploid and haploid thalli are different - heteromorphic
2. Location of gametangia
    a. If single thallus produces both sperm and eggs - homothallic
    b. If eggs and sperm borne separately - heterothallic
3. Ploid/structures produced
    Alternation of generations said to occur where we have n and 2n thalli Reproductive body of n thallus is gamete, thus n thallus is gametophyte. Reproductive body of a diploid thallus is spore, thus 2n thallus is sporophyte.
4. Gamete form
        Green algae exhibit all combinations of gamete types from isogamy to heterogamy.
    a. Isogamy - gametes are indistinguishable, both motile.
    b. Heterogamy: gametes are distinguishable - 2 types.
        i. Anisogamy - both motile, one small (sperm) one large (egg).
        ii. Oogamy - only one motile - sperm, one non-motile. very large (egg).
5. Gametangia
    a. Male gametangium - antheridium
    b. Female gametangium
        i. oogonium if single cell
        ii. archegonium if multicellular.
6. Zygotes may form a thick-walled resting zygospore.

A. Class Charophyceae
    1. Spirogyra
    Common filamentous alga of ponds and streams. Unbranched. Chloroplast one or more spirals. Asexual - fragmentation. Spores rarely formed. Sexual - isogamous, conjugation. Conjugation tube - with passage of protoplast. zygote - zygospore - overwinter - meiosis - 1 develops, 3 degenerate.
    2. Zygnema
    3. Coleochaeta
    4. Order Charales
        a. Chara and Nitella - Stoneworts Large branching (green) algae of fresh and brackish water. Resemble higher plants in appearance. Cell walls become impregnated with lime - very coarse - contribute to marl formation. Gametangia surrounded by sterile jacket of cells.
    5. Desmids
        Hemicells, isthmus.
        a. Examples:
            i. Closterium, large crescent-shaped desmid.
            ii. Cosmarium, bar-bell shaped desmid; flattened cells which show desmid semicell construction, isthmus contains the nucleus, cell is symmetrical with two pyrenoids in each half.
            iii. Desmidium, filamentous desmid.
            iv. Micrasterias, deeply incised, plate-like desmid.
            v. Staurastrum desmid, usually with three radiating arms at the distal end of each semi-cell.

B. Class Ulvophyceae
    1. Cladophora branching filaments; showing structure of branched filaments, each cell of which has several nuclei.
    2. Ulothrix
        Fw alga, often growing in flowing streams. Has holdfast. Forms filament. Each cell has large collar-shaped chloroplast. Asexual reproduction - quadri flagellated zoospores (1-32) escape through pore - swim then settle down and become holdfast, and form new filament - also form aplanospores. Sexual reproduction-Isogamous and heterothallic zygote -> zygospore -> meiosis -> 4-16 zoospores.
    3. Ulva - notable because of isomorphic alternation of generations
    4. Acetabularia - notable as 2n thallus, with only gametes n
    5. Codium - Large velvety tubular marine alga.
C. Class Chlorophyceae
    1. Chlamydomonas
        Unicellular flagellates of fw., soil, snow banks. Asexual reproduction - protoplast divides into 2-16 daughter cells, which develop cell wall, flagellae, then escape from parent cell. Sexual - isogametes, entire cells fusing - 4-flag. zygote. Zygospore - meiosis - mitosis? - liberated zoospores.
    2. Chlorella
    3. Pleurococcus (= Protococcus)
        Common in terrestrial habitats. Single celled - sometimes forms colonies. Chloroplast large, occupies most of cell. Cell division.
    4. Pediastrum - nearly flat, stellate colonies one cell in thickness; coenobium of polygonal cells arranged in a stellate plate.
    5. Hydrodictyon
    6. Volvocine line
        a. Volvox
    Colonial flagellate with 800-60,000 cells. Form is a hollow ball with well developed cytoplasmic strands between cells.
    Reproduction - certain cells of colony enlarge in diameter,-gonidia - enter sphere - develop either sexually or asexually, depending on season.
    Spring and Summer - asexual, - many mitotic divisions - ball invaginates and turns inside out, flagellae develop on outside, colony liberated from parent colony through hole.
    Late season - sexual reproduction - oogamous and homothallic or heterothallic depending on species. Some gonidia form ova, others divide to form clusters biflagellated sperm. When this cluster nears an egg, the sperm separate and swim to the egg, still inside the parent colony. Fertilization occurs, zygospore forms, released by death of parent colony, usually when winter sets in. Germinate following spring with meiotic division forming 4 zoospores, or 1 zoospore with decay of 3 nuclei.
        b. Gonium - 4-16-celled colonies; cells arranged in symmetrical patterns.
        c. Pandorina - subspherical colonies with 16 pyriform cells.
        d. Eudorina - spherical colonies, containing 32 or more spherical cells.
    7. Oedogonium
    Small permanent ponds slow streams, Often epiphytic. Holdfast. Single reticulate chloroplast. Apical caps often form from lengthening of filament. Asexual reproduction - zoospores, aplanospores, akinetes. Zoospores only in cells with apical caps. Cell wall breaks at junction with apical cap to liberate the zoospore. New filamentous forms, with holdfast.
    Sexual reproduction - oogamous with homo- or heterothallic plants. Antheridia shorter than most other cells. 1-2 sperm/cell. Oogonia much larger swollen compared with most cells. Zygote-zygospore - meiosis - 4 zoospores.
    8. Scenedesmus - four-celled colonies.