Phylogenetic comparison of rbcL gene sequences between Spirogyra, Zygnema and Sargassum Polycystum voucher species

Abstract

The chloroplast gene markers, such as rbcL, psaA, and atpB serve as valuable tools for DNA barcoding and species identification in algae. In this study, the rbcL gene was selected as the primary genetic marker due to its high degree of conservation across evolutionary timescales, making it particularly suitable for resolving phylogenetic relationships. Molecular analyses reveal that Spirogyra and Zygnema share a recent common ancestor and belong to the same evolutionary lineage within the green algae (Chlorophyta). Phylogenetic reconstruction indicates that Spirogyra represents a more basal or ancestral position relative to Zygnema within this clade. In contrast, Sargassum polycystum voucher (a brown alga belonging to the Phaeophyceae) falls into a distinctly separate lineage, consistent with the deep evolutionary divergence between green and brown algae. Comparative rbcL sequence analysis shows that the split between the green algal lineage (Spirogyra and Zygnema) and the brown algal lineage (Sargassum polycystum voucher) occurred very early in eukaryotic evolution. There is no close phylogenetic relationship between these groups, reflecting their placement in entirely different major clades Chlorophyta (green algae) and Stramenopiles (which includes brown algae). The molecular data highlight polyphyly within several traditionally classified algal taxa, underscoring the need for comprehensive taxonomic revision based on modern phylogenetic evidence. From the phylogenetic investigation there is divergent happed (0.08) but not deep divergent happed among green and brown algae.