New observations on the diatom genus Druehlago (Bacillariophyta) and description of two new species from South Africa

Two new species of the previously monospecific diatom genus Druehlago were discovered during the ongoing studies exploring the epizoic and epiphytic diatom flora of the Southern African coasts. These species are formally described here as D. craspedostauriformis sp. nov. and D. lobbanii sp. nov. Detailed morphological examination using both light and scanning electron microscopy revealed wedge-shaped frustules with a central constriction containing multiple lenticular chloroplasts, as well as heteropolar valves with wider headpoles and biarcuate raphes, typical of Druehlago. A stauros narrower than the fascia, a feature not yet reported from Druehlago but typical of the morphologically similar genus Craspedostauros, was observed in D. craspedostauriformis. Apart from the presence of a stauros, the latter species can be easily distinguished from other Druehlago members by its large size, low stria density, externally raised raphe-sternum, and girdle bands with a crenate pars interior. Although the gross morphology of D. lobbanii strongly resembled that of D. cuneata, the two species can be distinguished based on clear differences in size and stria density. Moreover, whereas shallow septa run along the almost entire length of the girdle bands in D. cuneata, they are absent in D. lobbanii. Based on the new findings and observations, the taxonomic status of the genus Druehlago and its morphological and ecological similarity to Craspedostauros and Achnanthes are discussed and evaluated.