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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 rbcL, psbC 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. [ABSTRACT FROM AUTHOR]

The current study focuses on the biological diversity of two strains of Antarctic diatoms (strains IMA082A and IMA088A) collected and isolated from the Ross Sea (Antarctica) during the XXXIV Italian Antarctic Expedition. Both species presented the typical morphological characters of the genus Craspedostauros: cribrate areolae, two "fore-and-aft" chloroplasts and a narrow "stauros". This classification is congruent with the molecular phylogeny based on the concatenated 18S rDNA-rbcL-psbC alignment, which showed that these algae formed a monophyletic lineage including six taxonomically accepted species of Craspedostauros. Since the study of the evolution of this genus and of others raphe-bearing diatoms with a "stauros" is particularly challenging and their phylogeny is still debated, we tested alternative tree topologies to evaluate the relationships among these taxa. The metabolic fingerprinting approach was implemented for the assessment of the chemical diversity of IMA082A and IMA088A. In conclusion, combining (1) traditional morphological features used in diatoms identification, (2) phylogenetic analyses of the small subunit rDNA (18S rDNA), rbcL and psbC genes, and (3) metabolic fingerprint, we described the strains IMA082A and IMA088A as Craspedostauros ineffabilis sp. nov. and Craspedostauros zucchellii sp. nov. as new species, respectively. [ABSTRACT FROM AUTHOR]