This work characterizes a unicellular cyanobacterium with nearly spherical cells and thin-outlined sheaths forming coherent packets that grows on rocky substrates in semiarid areas. Analysis of the 16S rRNA gene sequence and its secondary structure, as well as the internal transcribed spacer sequences and morphological and ecological features, revealed a unique position within the Chroococcales and led to the proposal of a new genus, Chalicogloea gen. nov., represented by the species Chalicogloea caespitosa gen. nov., sp. nov.