(cyanophyta) Blue-green algae; have no distinct nucleus or chloroplasts and do not reproduce sexually; contain chlorophyll a and can carry out oxygenic photosynthesis; the only organisms that fix both carbon dioxide and nitrogen; they are not true algae, but related to bacteria.

A phylum of oxygenic photosynthetic bacteria comprised of unicellular to multicellular bacteria possessing CHLOROPHYLL a and carrying out oxygenic PHOTOSYNTHESIS. Cyanobacteria are the only known organisms capable of fixing both CARBON DIOXIDE (in the presence of light) and NITROGEN. Cell morphology can include nitrogen-fixing heterocysts and/or resting cells called akinetes. Formerly called blue-green algae, cyanobacteria were traditionally treated as ALGAE.