The Reappearance of An Extremely Rare and Critically Endangered Nitella translucens (Charophyceae) in Poland 1 .

We report the reappearance of the rare charophyte Nitella translucens in Poland. It was identified in the soft-water lobelian Lake Jelen (North Poland) during 2013 and 2018 phytolittoral surveys. This species is considered critically endangered in various European countries and was previously classified as extinct in Poland. Its occurrence was confirmed using morphological and molecular data (ITS1-18S, ITS2-28S, rDNA, and rbcL). The N. translucens occupied similar to 20% of the lake bottom, at depths of 1.5-6.5 m, water pH 7.5-8.6, conductivity of 59-66 mu S center dot cm(-1), and total nitrogen and phosphorus during growing season in the range of 1.1-1.4 mg center dot L-1 and 0.07-0.1 mg center dot L-1, respectively. It co-occurred mainly with plant species typical for lobelia lakes: Isoetes lacustris, Littorella uniflora, and Myriophyllum alterniflorum, as well as Ceratophyllum demersum and Elodea canadensis, which are characteristic for eutrophicated waters. It appears that N. translucens may thrive in lobelia lakes during their transformation to more eutrophic states.