The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of species in the group varies from about 14 to 26. Together with the much larger sister taxa Rhodophyta (red algae) and Viridiplantae/Chloroplastida (green algae and land plants), they form the primary algae clade Archaeplastida.

The glaucophytes are of interest to biologists studying the evolution of chloroplasts as they may be similar to the ancestral algal type that led to the red algae and green plants, i.e. glaucophytes may be basal archaeplastids.

Unlike red and green algae, glaucophytes only have asexual reproduction.

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