Numerous species ofEunotiaEhrenb., widely distributed in the world flora, prefer acidic, dystrophic or oligotrophic freshwater habitats with low conductivity and usually occur in epiphytic or epilithic hydrotopes. In Ukraine, only 32 species and eight varieties ofEunotiawere known until this study. For the first time, 9 more species have been recorded mainly from the Cheremsky Nature Reserve, located in Ukrainian Polissya. New findings include 2 species widely distributed in the world flora on most continents and 7 rare species known from several locations, among themE.genuflexa,E.jarensisandE.ruzickae, which are probably European endemics as they have not been reported from other continents. For the present time in the Cheremsky Nature Reserve, the 20 species recorded here, the highest species richness ofEunotiain Ukraine, bring the total number ofEunotiain Ukraine to 41 species, which comprises only 7% ofEunotiaspecies in the world flora. This is indirect evidence of insufficient investigation of the wetlands in Ukraine whereEunotiausually is represented with high species richness. Several definitions are suggested to describe morphological features that are peculiar to the diatom frustule particular to theEunotiaspecies. The genus Eunotia possesses a mirror-symmetric,mantle-offset,brevisslit raphe system, which may or may not haveterminal raphe fissures. Morphological analysis provided in this study revealed the absence of terminal raphe fissures for many species ofEunotia. Instead, the distal ends of the raphe slits finish on the outer valve surface by funnel holes, sometimes pore-like ones, connected with the helictoglossae. However, in the literature those distal ends of the raphe slits were described erroneously as terminal raphe fissures. For the first time different types of raphe system are grounded. Two speciesEunotiaimplicataNörpel-Schempp et al. in Alles et al. andEunotiaincisaW. Smith ex Gregory were lectotypified.
