Neighbor-joining tree of the 16S-23S rRNA ITS1 sequences (length, 266 to 288 nucleotides) of A. flos-aquae colonies from the Baltic Sea (BS), Pojo Bay (PB), Lake Lohjanjärvi (LJ), Lake Hiidenvesi (HV), Lake Kirkkojärvi (KJ), and Lake Tuusulanjärvi (TJ) together with sequences (underlined) of strain 313 from Lake Tuusulanjärvi and reference A. flos-aquae sequences (underlined) (GenBank accession numbers) of strains 202 (AJ293198) from Lake Vesijärvi (VJ), TR183 (AJ293212) from the Baltic Sea, and 326b (AJ293200) and 326a (AJ293199) from Lake Lohjanjärvi. The dominating ITS1-S allele in the Baltic Sea is shown in bold type. Three subgroups, ITS1-Sb, ITS1-Sc, and ITS1-Sa, are indicated (for details, see the text). The scale bar indicates branch length, showing 0.1 nucleotide substitution per site. Only bootstrap values of >50% are shown.