Fig. 3.

Thalli and cells of freshwater Ulva flexuosa. Herbarium sheet of Ulva with branched thallus (arrow) (a). Juvenile thalli with calcium carbonate crystals on the surface (arrow), as seen in stereoscopic microscopy (b). Surface of thalli with rounded cells (black arrow) and CaCO₃ crystals (white arrows), as seen in scanning microscopy (c). Formation of proliferations from a swollen cell (arrow) in the central parts of the thallus, as seen in confocal microscopy (d). Cup-shaped chromatophore with 2–4 pyrenoids (arrows), as seen in light microscopy (e). Lugol’s iodine-stained pyrenoids (arrows) in the proximity of a chromatophore, as seen in light microscopy (f). Photo credits: a–f Andrzej S. Rybak