ostenfeldii and A. peruvianum. Phylogenetic analysis of rDNA sequences from the A. ostenfeldii selleck kinase inhibitor or A. peruvianum cultures examined in this study revealed a complex genetic structure, consisting of six distinct, but closely related groups. A detailed qualitative and quantitative analyses of isolates belonging to four of these groups showed that the diagnostic morphological characters (shape differences in the 1′,
s.a. and 6″ plates) used to define the original species were more variable than previously assumed, exhibiting extensive intra- and inter-strain variability. Instead of the morphological features being consistently associated with a given group, as would be expected if A. ostenfeldii and A. peruvianum were distinct species, each group examined contained strains morphologically MI-503 identified as either A. ostenfeldii or
A. peruvianum. In group 1, for instance, Baltic A. ostenfeldii and North American A. peruvianum strains (as identified by Kremp et al. 2009, Borkman et al. 2012, Tomas et al. 2012) form a monophyletic subgroup in the phylogenetic tree (Fig. 1). Two nearly identical sequences were obtained from A. ostenfeldii (AOKAL0909) and A. peruvianum (e.g., AP0905). Also, strains from the type localities of A. ostenfeldii and A. peruvianum were closely nested in the same phylogenetic group, group 6. Strain IMPLBA033, which represents the type location of the species in Callao, Peru (Balech and de Mendiola 1977) and which is morphologically in accordance with the A. peruvianum description, appears as the immediate neighbor of AONOR4, an A. ostenfeldii strain isolated from the location of the A. ostenfeldii redescription in Norway (Balech and Tangen 1985). The strain AOIS4 from the Iceland where Paulsen first found the species, was nested in group 5. AONOR4 in contrast, more closely resembles the description of A. peruvianum than the type described from the same location. Thus, though 上海皓元 the A. ostenfeldii and A. peruvianum
morphotypes as originally described appear distinct, their often nearly identical rDNA sequences indicate they represent the extreme ends in a continuum of A. ostenfeldii morphotypes. Consistent with this conclusion, the isolates examined in this study often showed a combination of the type A. ostenfeldii and A. peruvianum morphologies. Morphological characters were generally not consistently distributed. AONOR4 has some features that are typical for A. peruvianum such as small cell size and a predominantly A-shaped s.a. plate, which is not in accordance with what Balech and Tangen (1985) observed in field samples, collected from the same location. Cells of the Peruvian strain, on the other hand, were not particularly small as originally reported in the species description. The most inconsistent character, considered diagnostic in the original description, is the curved right anterior margin of the 1′ plate of A. peruvianum.