Phylogenetic position of the diatom genus Geissleria Lange-Bertalot & Metzeltin and description of two new species from Siberian mountain lakes

Two new Geissleria species from Siberian mountain lakes Baikal and Frolikha are described based on molecular and morphological data. The two new species are Geissleria baicalosimilis Kulikovskiy, Gusev, Andreeva & Annenkova sp. nov. and G. frolikhiensis Kulikovskiy, Gusev, Andreeva & Annenkova sp. nov. According to partial 18S rDNA and rbcL gene fragment analyses, Geissleria does not belong to the large catch-all genus Navicula as it was previously thought. Morphological features such as slit like areolae without hymenes, presence of one isolated pore near the central nodule and presence of props in areolae and an annulus structure support this conclusion. Plastid morphology of Geissleria species is typical for the Cymbellales, with one large chloroplast divided into two plates lying one against each valve, connected by a broad column. All of our data show that Geissleria is most closely to the genus Placoneis, with which they share naviculoid symmetry. Given these results, Geissleria should be included in the order Cymbellales.