Charophyte green algae (CGA) evolved strategies to survive on land and gave rise to the evolution of Embryophytes, which inherited fundamental traits of their algal ancestors, such as a complex polysaccharide-rich cell wall. Members of early- (Klebsormidophyceae) and late-diverged (Zygnematophyceae) CGA occur worldwide in terrestrial habitats. However, knowledge on the contribution of their cell wall properties to survive terrestrial conditions such as poor water supply is very limited. The present PhD thesis shows that filamentous terrestrial CGA modulate their cell walls in response to environmental stress and/or the developmental stage (e.g. during pre-akinete and aplanospore formation). Short-term desiccation stress induces incorporation of (1->3)--glucan (callose) into undulating cross cell walls of Klebsormidium spp. During desiccation-rehydration cycles, callose deposition helps preventing structural damage of Klebsormidium cells resulting in maintenance of a higher photosynthetic performance compared to Zygnema, which lacks this protection mechanism. Zygnema follows another strategy: vegetative cells develop with age into specialised resistant cells (termed pre-akinetes), which show a higher resistance against water shortage when compared with untransformed cells. Pre-akinete formation includes a reorganization of cell ultrastructure and changes the cell wall composition, e.g. by increasing the pectin fraction, which is considered to increase the water holding capacity of filaments. During cell growth, both Klebsormidium and Zygnema modify their complex hemicellulose network by transglycosylation in specific cell wall areas. In contrast, old thick-walled cells and pre-akinetes lack transglycanase activity, underpinning the pre-akinetes decreased metabolic activity and role as resting cells. Another adaptation to the terrestrial environment was found in the filamentous GCA Zygogonium ericetorum, which is common in acidic habitats with increased Fe and Al concentrations. Formation of vegetative aplanospores facilitates removal of excessive iron from the protoplast. Moreover, aplanospore germination enables filament growth despite high aluminium concentrations in the parental cell wall and terrestrial habitat.