I. Characteristics

A. External morphology.
    Single cells, colonies, filaments. Colonial forms - flat, spherical, elongate, cubical or amorphous. Gelatinous sheath of individual. cells may remain distinct, or may fuse into gelatinous matrix. A filament may consist of one or more chains of cells. Each chain is termed a trichome.

B. Motion
    There are no organelles for locomotion. Some forms - Ex. Oscillatoria - can move - forward and backward, or with a nodding motion.

C. Pigments
    All photosynthetic organisms have chlorophyll and associated carotenoid pigments. Cyanophytes also have additional accessory pigments termed phycobilins. They are the phycocyanins and phycoerythrins. The blue-green algae are most often that color, but may also be purple, red, yellow, brown, or blackish.

D. Cytology
    Typically a protoplast surrounded by a cell wall enclosed in a gelatinous sheath. Protoplast consists of colorless central body and pigmented outer chromoplasm. Central body is rich in chromatin - resembles a nucleus. Also contains most of the ribosomes. The pigments are scattered through the chromoplasm. In some blue-green, the photosynthetic pigments are arranged in flattened discs, known as thylakoids. Cell div. is amitotic.

E. Food reserves
    Main food is cyanophycean starch - glycogen and protein

A. Fragmentation of colonies

B. Spores

1. Akinete - enlargement of a single vegetative cell, with thickening of cell wall. Entire protoplast is contained in an akinete. This is a resistant resting stage.
2. Sporangiospores - Formed by many div. of protoplast, so that original cell wall becomes a sporangium containing spores.
Both akinetes and sporangiospores are nonmotile.
C. Other structures
1. Heterocysts - enlarged clear cells which in some cases are functionless, others, they serve as fragmentation points; other possibilities.
2. Separation discs - double concave area of filament containing gelatinous subst. - fragmentation area. Sections between discs are termed hormogonia. Also sections between heterocysts and/or separation disks can be called hormogonia.
3. NO SEXUAL Reproduction

IV. Carbonate deposition
    Complex balance in water between CO₂, carbonic acid (H₂CO₃) and dissolved bicarbonates. As CO₂ is used up by algae, etc., dissolved bicarbonates are changed to insoluble carbonates. Thus algae contributes to the deposition of carbonates, which accumulate at the bottom of some lakes and bogs as marl. This is thought to have been important in formation of many limestone deposits.

V. Thermal algae
    Blue-green algae of many types survive well at temperatures well over 50C., which is above the temperature most organisms can survive. Blue-green algae are found in hot springs around the world. Some of the algae in Yellowstone live in a normal temperature 85C, while overflow water 90C - boiling point at that altitude. The spectacular colors of the springs at Mammoth Hot Springs, etc., are due mainly to blue-green algae. They also contribute to the mineral depositions so characteristic of the springs.

VI. Stromatolites
    Calcium bound by colonies of cyanobacteria - shallow pools in hot climates. Said to be 2.7 billion years old!

VI. Representative Genera

A. Gloeocapsa
    Common on damp rocks. Spherical cells in amorphous colonies of >50 cells. Sheath color variable - red, blue, violet, brown, yellow. Reproduction - cell division and colony fragmentation.
B. Merismopedia
    Free-floating colonies in many types of lentic comm. - one cell thick, up to many hundred in colony. - rectangular shape with regular vertical and horizontal rows of cells. Reproduction as Gloeocapsa.
C. Oscillatoria
    Very common. Well defined unbranched filaments may be simple or interwoven into dense mat. Movement present. Reproduction - fragmentation at separation discs; cell div. May be thermal algae.
D. Lyngbya
E. Nostoc
    Occurs in soil and in fresh-water Form: twisted trichomes with individual sheath, often aggregated into large gelatinous balls. Heterocysts present, fragment here. Akinetes formed when colony matures.
F. Anabaena
    Free-floating colonies in f.w. lentic habitats, similar to Nostoc, except large balls are not normally formed. Also trichomes usually not as contorted. Cells more elongate, less rounded.
G. Gloeotrichia
    With akinete.
H. Rivularia
    No akinete
I. Microcystis

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