Closteriopsis acicularis (G. M. Smith) Belcher et Swale is a fusiform algaclosely related to Chlorella kessleri Fott et Novakova (Chlorophyta, Trebouxiophyceae)

Complete nuclear 18S rRNA and chloroplast 16S rRNA coding sequences of the fusiform green alga Closteriopsis acicularis (G. M. Smith) Belcher et Swale (Chlorophyta) were used to determine its phylogenetic position within the Chlorophyta. Phylogenetic trees inferred from both genes show that C. acicu laris is most closely related to Chlorella kessleri Fott et Novakova (Trebo uxiophyceae) and does not belong to the family Selenastraceae (Chlorophycea e) as proposed previously. Despite its morphological distinctness, C. acicu laris has to be placed close to the genus Chlorella Beijerinck, and especia lly to C. kessleri. The chloroplast 16S rRNAs of C. acicularis and C, kessl eri possess a unique insertion resulting in an additional AT-rich helix in a length-conserved region of the gene. A close relationship to the genus Ch lorella is further confirmed by the pyrenoid ultrastructure. The 16S rRNA g ene of C. acicularis contains a group I subgroup IA3 intron which is most s imilar to the first intron in the corresponding gene of Chlamydomonas palli dostigmatica King (Chlorophyta). In helix P6. the intron carries an additio nal extension related to intron-encoded endonucleases of the LAGLIDADG fami ly. It is the first group I intron reported in chloroplast 16S rDNA of a sp ecies other than Chlamydomonas.