Phylogenetic relationships among algae based on complete large-subunit rRNA sequences

The complete or nearly complete large-subunit rRNA (LSU rRNA) sequences wer e determined for representatives of several algal groups such as the chlora rachniophytes, cryptomonads, haptophytes, bacillariophytes, dictyochophytes and pelagophytes. Our aim was to study the phylogenetic position and relat ionships of the different groups of algae, and in particular to study the r elationships among the different classes of heterokont algae. In LSU rRNA p hylogenies, the chlorarachniophytes, cryptomonads and haptophytes seem to f orm independent evolutionary lineages, for which a specific relationship wi th any of the other eukaryotic taxa cannot be demonstrated. This is in acco rdance with phylogenies inferred on the basis of the small-subunit rRNA (SS U rRNA), Regarding the heterokont algae, which form a well-supported monoph yletic lineage on the basis of LSU rRNA, resolution between the different c lasses could be improved by combining the SSU and LSU rRNA data. Based on a concatenated alignment of both molecules, the phaeophytes and the xanthoph ytes are sister taxa, as well as the pelagophytes and the dictyochophytes, and the chrysophytes and the eustigmatophytes. All these sister group relat ionships are highly supported by bootstrap analysis and by different method s of tree construction.