GATAs are evolutionarily conserved zinc-finger transcription factors from eukaryotes. In plants, GATAs can be subdivided into four classes, A – D, based on their DNA-binding domain, and into further subclasses based on additional protein motifs. B-GATAs with a so-called LLM-domain can already be found in algae, but bryophytes and angiosperms also contain B-GATAs with a HAN-domain. The angiosperm B-GATA family is expanded and can be subdivided into family members with either a HAN- or an LLM-domain. The B-GATA family in the liverwort Marchantia polymorpha and the moss Physcomitrium patens is restricted to one and four family members, respectively, and all family members contain a HAN- as well as an LLM-domain. Here, we characterize mutants of the single B-GATA from Marchantia polymorpha. We reveal that this mutant has defects in thallus growth and in gemma formation. Transcriptomic studies uncover that the B-GATA mutant displays a constitutive high-light stress response, a phenotype that we then also confirm in mutants of Arabidopsis thaliana LLM-domain B-GATAs, suggesting that the B-GATAs have a protective role towards high-light stress.