A case of mis-identification

by Mike Samworth

After looking at a sample taken from the pond in the grounds of where I work, I was puzzled by some green algae. There seemed lots of this particular species in the sample and so I set about trying to identify it. Rather small in size and somewhat club-shaped it wasn't familiar at all.

Flicking through various books in a quite unsystematic way I had narrowed it down to two, Characiopsis sp. or Characium sp.

Characiopsis (left) and Characium (right).

I wasn't particularly confident with either genus but since it turned out that the former has no starch formed, an Iodine solution test should do the trick. So I made a note to get some from work. By the time I had, a second look at the sample revealed some further development. The cells were no longer singular and were in fact two or three cells long; this was a filamentous alga! Further features noted, such as concentric rings around one or two of the cells made me realise this was in fact Oedogonium.

There are over two hundred species in this genus. It is a filamentous type where the cells divide by a characteristic method. It is this division that causes the rib-like bands at the end of the cell. The number of "ribs" present indicates the number of times the cell has divided. Oedogonium produces motile spores and these eventually settle down and germinate to form new plants. It is this stage that I had come across, the so called germlings. They looked peculiar at one end because they have a star-shaped disc or holdfast.

Oedogonium germling with holdfast, and first division.

This just goes to show how easily we fall into too speedy an identification. Also how important it is to make observations over a period of time before coming to any hard and fast conclusions. Above all it is but a learning experience and a great deal of fun, and that is what really matters. Oh, this is how it normally looks!

If any reader wishes to ask about any of the above, or to comment, please do get in touch by contacting meComments to the author sent via our contacts page quoting page url plus : ('msamworth','')"> Mike Samworth.


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