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We analyzed the ITS2 primary and secondary structure (including Compensatory Base Changes ( CBCs)) of 17 new Dunaliella strains (11 D. viridis, two D. tertiolecta, and four Dunaliella sp.), and compared these with other Dunaliella sequences available from the ITS2 database to circumscribe their taxonomic position. The ITS2 primary and secondary structure analysis positioned the majority of D. viridis strains in four main clades, showing that D. viridis is polyphyletic. The detection of at least one CBC among these clades strongly suggests that they could correspond to different biological species. Unexpectedly, while D. viridis var. euchlora ( CCAP19/21) was positioned within the subgenus Dunaliella, D. viridis var. palmelloides ( CCAP11/34) was positioned clearly outside this subgenus, suggesting that this taxon may not be properly placed in Dunaliella. Furthermore, the detection of at least three compensatory base changes ( CBCs) between D. viridis var. palmelloides ( CCAP11/34) and the other strains analyzed, confirm that this strain is a different species. For these reasons we propose re-naming D. viridis var. palmelloides ( CCAP11/34) to incertae sedis, and D. viridis var. euchlora ( CCAP19/21) to Dunaliella sp. Therefore, the ITS2 primary and secondary structure data suggest a taxonomic re-structuring of D. viridis. [ABSTRACT FROM AUTHOR]