Gunnera is the only genus of flowering plants to form a symbiotic association with cyanobacteria (blue-green algae). The cyanobacteria component is called Nostoc (sometimes called "star jelly" because of the gelatinous colonies that Nostoc forms in moist environments). Nostoc can live in specialised cells (called hetetocysts) at the leaf base of gunnera plants. These heterocysts are like the root nodules on legumes, and are able to fix nitrogen which can then be used by the host gunnera plant.