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NOTE: this key is a bit different from the traditional dichotomous key; I've based it on how I think I make IDs myself, at least in the early stages.
It does not cover all genera listed in the "Freshwater Algal Flora of the British Isles", only more common ones, and mainly ones I have images of.
Inevitably, with more difficult specimens, you may need to use a good traditional key also. See also links to other web-based keys listed on the 'links' page.
I'd appreciate any feedback from anyone trying to use it: does it make sense? are any parts ambiguous?

Algal Search Sitemap and quick links
Jump to: (filename)	start  (search1)	filaments (search2)	branched +chloroplast (search3)	unbranched +chloroplast (search4)	unbranched cyanobacteria (search5)	branched cyanobacteria (search6)
		Colonies and coenobia +chloroplast (search10)	planktonic, with sheath   (search11)	planktonic, without sheath   (search12)	attached cushion (search13)	attached, flat plate (search13)	attached, sheath (search14)
		Colonies and coenobia : Cyanobacteria (search21)	planktonic, with sheath (search21)
		Unicells (under development)	+ chloroplast(s) (search31) (under development)	Desmids (searchdesmid)	non-flagellate cells without case (under development)	in silica case = diatoms (under development)	flagellate cells (under development)
			no chloroplast: Cyanobacteria (search31)

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Specimen is a:	filament (2 or more cells linked in a linear series)
	colony (more than 2 cells in a group),
	or sometimes more precisely a coenobium: a definite number of cells, usually a multiple of 4, often arranged in a regular manner
	Unicell one (or two) cells only; sometimes divided into semicells

John Kinross