Abstract
The macroalgae representing the cosmopolitan Ulva flexuosa Wulfen species have been found in inland water ecosystems of Europe since the mid-1800s. The presence of the Ulva genus in waters of inland salt marshes was explained by high salinity of water in such systems. However, Ulva flexuosa thalli were found in lakes and rivers having no supply from strongly mineralized sources, either of natural or anthropogenic origin. The study focused only on populations of Ulva flexuosa subsp. pilifera (Kűtz.) M.J. Wynne and Ulva flexuosa subsp. paradoxa (C. Agardh) M.J. Wynne occurring in inland ecosystems isolated from seawater. The differentiation of inland U. flexuosa subsp. pilifera and subspecies paradoxa was assessed by using classical morphological data and molecular techniques. We found that only two subspecies of Ulva flexuosa Wulfen occur in inland water ecosystems of Poland. On the basis of the analysis combining morphological features with the ITS region and rbcL gene sequences, a small degree of differentiation of the two inland taxa was demonstrated. These two subspecies have high differentiation of the habitat niches. U. flexuosa subsp. paradoxa settled in habitats featuring high salinity levels, and the second subspecies pilifera occurred only in fresh waters.