Taxonomy and fine structure of a marine diatom Achnanthes grunowii, nom. nov.

Achnanthes grunowii Toyoda & D. M. Williams was first described by Grunow in Cleve and Grunow (1880), as a variety of A. javanica Grunow, A. javanica var. rhombica. It is shown that the valve face of this taxon is rhombic in shape, and there are marginal and terminal ridges as well as terminal orbiculi on the ARV. The striae stand in more than three rows between costae on the valve, and the areolae stand in more than four rows on the copulae. In contrast, A. javanica var. javanica has the marginal ridge but no terminal spine, and terminal orbiculi and striae stand in two rows on the valve and small areolae stand in two rows on the valvocopula. These features support the view that A. javanica var. rhombica should be considered an independent species. However, the specific epithet rhombica was used by Østrup (1910) and Meister (1937) in this genus. Hence the new specific epithet grunowii is selected.