Palaeoecological significance of the spores of the liverwort Riella (Riellaceae) in a late Pleistocene long pollen record from the hypersaline Lake Urmia, NW Iran

Spores of the liverwort Riella are documented in a long late-Pleistocene to early Holocene pollen record from the hypersaline Lake Urmia in NW Iran. The pollen record indicates that Riella aff. cossoniana Trab. has played an important role in the aquatic vegetation in the plains around Lake Urmia, particularly in the late Pleistocene. The concentration of Riella spores was greater during the high lake stands corresponding to the middle part of the last glaciations (MIS 3) and the upper part of the penultimate glaciations (MIS 6). The presence of Riella suggests that during these periods numerous brackish ponds and marshes developed on the present salt flats around the lake, creating suitable habitat for colonization. The spores of Riella can therefore be used as a palaeoecological indicator of lake level changes in saline lake environments situated in semi-arid regions.