Chara squamosa (Characeae, Charophyceae) in Serbia - insights from the taxonomic revision of the BEOU charophyte collection and recent field records

Chara gymnophylla is one of the first charophyte species reported for Serbia during the late 19th and the early 20th centuries, and at that time it was the second in terms of the frequency of its occurrence in the country. General taxonomic misinterpretations in the past resulted in the concealment of another species, C. squamosa, within the findings attributed to C. gymnophylla. In Serbia, Chara gymnophylla was treated as C. vulgaris var. gymnophylla, and as such was not listed as a species inhabiting the country. Recent improvements in the taxonomic concept for C. squamosa prompted a revision of the rich material of C. gymnophylla, C. vulgaris var. gymnophylla, C. vulgaris var. nitelloides, and C. rohlenae, deposited in the BEOU collection. The revision process was conducted concurrently with fieldwork and the collection of new material. Our study confirmed the presence of C. squamosa in Serbia for the first time. Based on numerous revised samples from the BEOU collection, as well as recently collected specimens, the species? continuous presence in Serbia since 1976 was confirmed. Chara squamosa and C. gymnophylla were thus added to the list of Characeae species inhabiting Serbia, and categorised as Critically Endangered according to the criteria outlined by IUCN. An overview of the biogeography, ecology and taxonomy of C. squamosa in Serbia is provided, particularly in relation to C. gymnophylla. The BEOU charophyte collection proved to represent a valuable and relevant resource for critical taxonomic revisions. The results presented in this study strongly encourage further studies on C. squamosa and C. gymnophylla distribution in the Balkan region and wider area in order to gain a deeper understanding of the species? ecology and the further improvement of their taxonomic concepts.