What are 'algae'?
The term 'algae' is one of convenience and it includes simple photosynthetic organisms not included among the mosses, liverworts (and other bryophytes) or the vascular plants. Strictly, the algae are either unicellular organisms or, if multicellular, then with one-celled sporangia (they never produce multicellular embryos inside the female reproductive organ).
In recent years, the simple division of the living world into ‘plants’ and ‘animals’ has been replaced by a more accurate and ultimately useful suite of kingdoms.
The eukaryotic algae (those with compartmentalised cells) are part of a diverse group of organisms called protists. The kingdom Protista (once included partly in the animal kingdom and partly in the plant kingdom) is now divided into a number of as yet not adequately circumscribed kingdoms.
The prokaryotic algae (the cyanobacteria) are included with bacteria in the kingdom Monera.
What do we mean by 'freshwater'?
We have used a very broad definition of 'freshwater', essentially equating it with 'non-marine'.
The marine environment is considered to be those areas influenced by the sea, i.e. under marine tidal influence. There are some intermediate habitats and we have used our discretion in such cases. Sometimes there is insufficient information provided to determine the habitat.
The widespread occurrence of saline and hypersaline lakes in Australia means that brackish and marine taxa may be found far inland. Once again we have used our discretion as to whether we include taxa or not (e.g. algae reported from Lake Wellington in Victoria have not been included since it is usually an estuarine lake that sometimes becomes almost fresh due to flood waters).
We have also included some algae that grow on soil, trees and other ‘non-aquatic’ habitats.