New finding of Vaucheria aversa Hassall (Ochrophyta, Xanthophyceae) in Ukraine

Vaucheria aversa (Xanthophyta) was recorded for the first time in Ukraine in Sula River, Hydrological Reserve «Artopolot», Poltava Region. It was found in benthos in spring (May 2020) in silty-sandy soil in shallow water. The material was collected and processed according to a common methodology. Sterile samples before the appearance of the gametengians were kept in natural water in petri dishes in well-lit places. This method of «coarse culture», in most cases, allowed to get gametangia within two weeks. The species identification was done with fertile filaments only. 4% formaldehyde solution was used for material fixation. Taxonomic identification of samples was done using a comparative and morphological methods, which includes analysis of morphological variability and verification of the consistency of the studied material with the diagnosis. Thalli of V. aversa are direct, branched, bisexual, 80–90 μm wide. Antheridia are cylindrical, tubular shape, pressed to the filament or slightly raised above it, 119–130 × 41–43 μm. Oogonia erect, sessile, ovoid to subspherical, sometimes placed in pairs, with a curved beak at the front, 190–230 × 140–163 μm. According to morphological characteristics this species is similar to another one from section Tubligerae Walz – V. fontinalis (Linnaeus) T.A. Christensen. Their distinctive and common features are as follows. Filaments of V. fontinalis are narrower (up to 75 μm) than V. aversa (up to 131 μm). Both species are characterized by oogonia grouped together in a row. Antheridia present in quantity 1 or 2 on both sides of oogonia. But the species are very different in size and shape of oogonia: in V. aversa they are sessile, located one at a time or less often two, extended near the base, sharply narrowed at the apex. The beak is directed straight or obliquely up, bent to the side of the oogonia body. In V. fontinalis oogonia are placed in one row, most often in the amount of 1-6, the beak tapers gradually. Anteridia are cylindrical, on short pedicel. V. aversa grew as a part of polyspecies complex of green algae together with representatives of such genera as Cladophora Kützing, Spirogyra Link and Mougeotia C. Agardh. V. aversa is widely distributed in continental water bodies of Europe, Asia and North America, Australia and New Zealand, but is firstly recorded in Ukraine.