Re-examination of Mereschkowsky's genus Tetramphora (Bacillariophyta) and its separation from Amphora

The raphid diatom genus Amphora has been subject to considerable revision over the previous 30 years, with many species transferred to newly created or existing genera. Despite these efforts, recent work has demonstrated that taxa presently assigned to the genus continue to be non-monophyletic and further revision is required. This investigation re-examines Mereschkowsky's genus Tetramphora, which he described as including all Amphora species with four chloroplasts, arranged in pairs linked by large pyrenoids. Although largely ignored over the last 100 years, recent work has shown that taxa aligning with Tetramphora are monophyletic and distinct from Amphora sensu stricto. Nine species belonging to Tetramphora are illustrated and described, based on light and scanning electron microscope observations, as well as a preliminary molecular phylogeny for the group. From these observations, we designate Mereschkowsky's T. ostrearia as the generitype of Tetramphora, recognize T. lineolata, and transfer the Amphora taxa, A. decussata, A. sulcata, A. rhombica, A. intermedia and A. securicula, and the Halamphora taxon H. chilensis to Tetramphora. In addition, three new species, T. fontinalis, T. lineolatoides and T. robusta, are described.