Molecular phylogeny of the marine diatom genus Druehlago (Bacillariophyceae) from Japan

SUMMARY The diatom genus Druehlago was established to differentiate the type species from Craspedostauros and Achnanthes , on the basis of unique heteropolar, cuneate frustules and numerous lenticular plastids. The phylogenetic placement of Druehlago has, until now, relied solely on morphological evidence, suggesting a close relationship with the genus Craspedostauros . In the present study, we discovered a population of Druehlago cf. cuneata along the coast of Japan and established a cultured strain. Molecular phylogenetic analysis based on rbc L, psb C and 18S rRNA genes was conducted to explore the phylogenetic position and classification of Druehlago . Our results revealed that D. cf. cuneata belongs to the Craspedostauros clade, but with weak statistical support, which is, in turn, sister to Achnanthes . Given the lack of support for various nodes within the Craspedostauros clade, constrained trees were constructed based on several hypotheses regarding the phylogenetic position of Druehlago . The hypothesis inferring monophyly of Druehlago and Achnanthes was statistically rejected, which highlights the close relationship between Druehlago and Craspedostauros . However, our topology tests provided no further resolution regarding the phylogenetic position of Druehlago within or outside Craspedostauros . Furthermore, the treatment of the specimens is discussed through a morphological comparison with the type of material.