Molecular Investigation of the Achnanthidium minutissimum Complex (Bacillariophyceae) from the Transbaikal Region with the Description of Three New Species

Representatives of the Achnanthidium minutissimum complex have been studied from the Transbaikal region, Russia. The Transbaikal region is known for its unique algal flora and high levels of endemism. Despite the group of monoraphid diatoms being studied quite extensively in this region in recent years, only four species of Achnanthidium have been reported so far. Three new species are described based on LM and SEM microphotographs and molecular data: Achnanthidium baicalonanum sp. nov., A. obscurum sp. nov. and A. angustum sp. nov. Comparison with similar species is given. The new species differ from other species of the genus by valve shape, striae and areolae structure, shape of external distal raphe ends and central area. According to molecular data, the new species form separate branches within the A. minutissimum complex. Ecological preferences of the new species are examined. All of the new species are only known from the Transbaikal region. This study contributes to the understanding of Achnanthidium taxonomy and biogeography and will be an asset to future biomonitoring studies.