Found this Pediastrum integrum C.W. Nägeli 1849 in a sample with almost nothing in it. And yes, Komárek and Jankovská (2001) tell that it’s common in oligotrophic and dystrophic cold and clear large and small lakes as well as small peaty basins. Everything fine so far.
What puzzled me was there also was P. angulosum (C.G. Ehrenberg 1834) ex G.G.A. Meneghini 1840, which Komárek and Jankovská (2001) describe as “rather alkalifilic and does not occur in peaty waters an acidic swamps.” But then again, I only saw two coenobia, one of each. In 25 ml. And of course they could occur simultaneusly. Water could be oligotrophic, but not so dystrophic and acidic, with some submersed waterplants too, so that they would both feel happy.
Wecktröm et al (2010) wrote a nice article about ecology of the Pediastrum in subarctic lakes. They mention both these species too. P. integrum was the only species in their study, for which they found similar distribution as the earlier studies. For P. angulosum they found that it was most abundant in lakes with the lowest pH and highest DOC concentration. But, then again, their most acidic was 6,4. So not that acidic anyway. Komárek and Jankovská (2001) write, that P. angulosum is known probably more in warm areas. But it’s here too, I can tell!
These species were easy ones to identify. More difficult it gets with the many variaties of P. boryanum. According to Komárek and Jankovská (2001) var. breviscorne and var. forcipatum have been seen in tropical countries and they think that data from these varieties from the northern countries very probably are other species. Well, well. Weckström & co write anyway that they have trust in their identification. I would – for my part – be very careful with these varieties.