Three New Diatom Species from Spring Habitats in the Northern Apennines (Emilia-Romagna, Italy)

Using light (LM, including plastid characterization on fresh material) and scanning electron microscopy (SEM), as well as a thorough morphological, physical, chemical, and biological characterization of the habitats, the present study aims at describing three species new to science. They belong to the genera <i>Eunotia</i> Ehrenb., <i>Planothidium</i> Round and L. Bukht., and <i>Delicatophycus</i> M.J. Wynne, and were found in two contrasting spring types in the northern Apennines. The three new species described differ morphologically from the most similar species by: less dense striae and areolae, and the absence of a ridge at the valve face-mantle transition (SEM feature) [<i>Eunotia crassiminor</i> Lange-Bert. et Cantonati sp. nov.; closest established species: <i>Eunotia minor</i> (Kütz.) Grunow]; narrower and shorter cells [<i>Planothidium angustilanceolatum</i> Lange-Bert. et Cantonati sp. nov.; most similar species: <i>Planothidium lanceolatum</i> (Bréb. ex Kütz.) Lange-Bert.]; barely-dorsiventral symmetry, set off ends, and lower density of the central dorsal striae [<i>Delicatophycus crassiminutus</i> Lange-Bert. et Cantonati sp. nov.; most similar species: <i>Delicatophycus minutus</i> M.J.Wynne]. Two of the three species we described are separated from the closest species by dimensions. Their description improved knowledge on two taxa (<i>Eunotia minor</i> s.l. and <i>Planothidium lanceolatum</i> s.l.) likely to be only partially resolved species complexes. We could also refine knowledge on the ecological profiles of the three newly-described species. <i>Eunotia crassiminor</i> sp. nov., as compared to <i>Eunotia minor</i>, appears to occur in colder inland waters with a circumneutral pH and a strict oligotrophy as well with respect to nitrogen. The typical habitat of <i>Planothidium angustilanceolatum</i> sp. nov. appears to be oligotrophic mountain flowing springs with low conductivity. <i>Delicatophycus crassiminutus</i> sp. nov. was observed only in limestone-precipitating springs, and is therefore likely to be restricted to hard water springs and comparable habitats where CO₂ degassing leads to carbonate precipitation. Springs are a unique but severely threatened wetland type. Therefore, the in-depth knowledge of the taxonomy and ecology of characteristic diatom species is important, because diatoms are excellent indicators of the quality and integrity of these peculiar ecosystems in the face of direct and indirect human impacts.