Two Zygnematophyceaen algae (sister-clade of the Embryophytes) were investigated: Mesotaenium endlicherianum SAG12.97 and Zygnema circumcarinatum SAG698-1b. The algae were grown on agar plates and submitted to osmotic stress for 6 or 25 hours by transferring them to a plates supplemented with either 0.8M mannitol or 0.15M NaCl. We investigated their osmotic response with the use of transcriptomics, proteomics, metabolomics, photophysiology analysis, sugar analysis, microscopy, and immunocytochemical glycoprotein analysis.