Rare Pediastrum species (Chlorophyceae) from Polish coastal lakes

An account is given of the occurrence of Pediastrum (Chlorophyceae, Sphaeropleales) in five eutrophic coastal lakes (Jamno, Bukowo, Gardno, Łebsko and Sarbsko) in northern Poland, together with morphological data of the species and more detailed taxonomic and ecological information for three taxa which appear to be rare world wide. These are P. musterii, P. orientale and P. alternans; the first is recorded for the first time from central Europe. P. orientale and P. alternans show considerable morphological variability under different environmental conditions, indicating the need for further studies. The studied lakes seem to be especially favourable for Pediastrum, with a total of eight species (15 taxa) in the phytoplankton noted during the summer. However, the relative frequency of the genus in the overall algal communities was low. The most frequent species were P. boryanum, P. kawraiskyi and P. duplex and these were accompanied by cyanobacteria, coccal green algae (Chlorophyceae, Chlorococcales) and diatoms (Bacillariophyceae). All the Pediastrum taxa were documented using LM and SEM.