LAUSR

Macroscopic fuzzy clumps of green filaments resembling filamentous algae were found on multiple sampling occasions in the water close to the shore of the extremely acidic (pH < 3) Hromnice Lake in Czechia. Microscopic investigation revealed that these filaments were moss protonemata. In order to identify the moss, we sequenced chloroplast (rbcL), mitochondrial (nad5), and nuclear (ITS2) molecular markers of these filaments. In addition, we sampled adult mosses growing on the wet substrate soaked with lakewater. The sequences of protonemata matched those of the adults, which were morphologically identified as Dicranella sp. Phylogenetic analysis of the rbcL gene showed a sister relationship with D. heteromalla, generally known for growing in acidic habitats, and other protonemata occurring in acidic rivers in Japan. The nad5-based phylogeny revealed that the studied protonemata belonged to the species D. cerviculata, and the same taxonomic affiliation was confirmed by the ITS2 rDNA sequence and its secondary structure. The extreme environment of Hromnice Lake prevents the further development of protonemata which, in turn, are capable of surviving acidic conditions in the prolonged protonemal stage. Due to their macroscopic similarity to filamentous algae, protonemata might be more common in extremely acidic waters than originally thought.