Census of Freshwater Algae in Australia
According to the classification system adopted by Day et al. (1995), there are 13 divisions of algae represented in Australian inland waters (a freshwater Phaeophyta has been discovered since publication of that checklist). Each division includes a wide range of vegetative and reproductive diversity, and in some cases almost identical taxa may reside in two different divisions: similar environmental pressures may have led to the evolution of similar traits in organisms with a fundamentally different origin.
The single cells, colonies or filaments are yellow to light brown. The cell wall always consists of two overlapping silica shells (like a petri-dish).
CHLOROPHYTA (GREEN ALGAE)
The single cells, colonies, filaments or more complexly structured algae are usually grass-green. Motile cells have usually two or four anterior flagella of equal length. This division includes many distinct evolutionary lineages.
CHRYSOPHYTA (GOLDEN-BROWN ALGAE)
The single cells, colonies or filaments are yellow, golden-brown or rarely green. Motile cells usually have two anterior flagella of unequal length.
The single cells are red, blue-green or olive-brown. All cells are motile, usually with two slightly unequal flagella.
CYANOBACTERIA (BLUE-GREEN ALGAE)
The single cells, colonies and more complexly structured algae are blue-green, brownish, olive-green or rarely bright green. The cells are without compartments (no membrane-bound organelles): in particular there is no nuclear region defined by a membrane and photosynthetic pigments are distributed throughout the cells (not in chloroplasts). Sexual reproduction and motile cells are absent.
The single cells are brown or brownish green. Motile cells have a prominent transverse furrow in which two flagella are inserted (one encircling the cell transversely, the other extending out from the cell).
The single cells are green (sometimes colourless) with a red 'eyespot'. The motile cells usually have two flagella inserted in a 'gullet' at the anterior end of the cell, one shorter flagella often non-emergent.
The single cells or colonies are blue-green. The pigments are held in symbiotic blue-green algal cells rather than chloroplasts (possibly representing an earlier stage in chloroplast evolution). The motile cells are dorsiventrally symmetrical with two lateral flagella.
PHAEOPHYTA (BROWN ALGAE)
Almost entirely containing marine species. The filaments are brownish or yellow-brown. Motile cells usually have two unequal flagella.
The single cells or filaments (sometime without cross-walls, i.e. siphonous) are green or yellow-green. Motile cells have two anterior flagella of unequal length.
The single cells, colonies or filaments are golden-brown. Motile cells have two more or less equal flagella and a thread-like organelle (the haptonema) between them.
Algae similar to Tribophytes but with a distinctive internal cell structure.
RHODOPHYTA (RED ALGAE)
Predominantly (c. 95% of species) marine. The single cells, filaments or more complexly structured algae are red, brown, olive-green or more rarely grass green. There are no motile cells in this division and sexual reproduction is often remarkably complex. Most have characteristic microscopic connections between the vegetative cells, although the blue-green alga Stigonema appears to have similar connections and the red alga Compsopogon has connections that are too small to be seen under normal light microscopy.