Epithemia fragarioides sp. nov. (Bacillariophyta): Formal recognition of a diatom widespread across Japan

SUMMARY We describe Epithemia fragarioides sp. nov., a diatom species from Japan. Our description is based on morphological analyses using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), supplemented by molecular phylogeny. Under LM, E. fragarioides has valves with a nearly straight ventral margin, a convex dorsal margin, narrow capitate apices, and distinctly separated areolae. SEM observations reveal that the areolae are slightly depressed below the valve face and exhibit occlusions with small projections. This fine structure is the most distinctive characteristic of this species compared to similar taxa, such as Rhopalodia michelorum and Rhopalodia tholulata . The ecological optimum of this species appears to be associated with neutral to slightly acidic wetlands with moderate electrical conductivity. Additionally, we relate our findings to the systematic understanding of the genus Epithemia / Rhopalodia .