glaucophyte

Glaucophyta, commonly called glaucophytes, is a small division of microscopic freshwater algae comprising a limited number of species in a few genera, including Cyanophora and Glaucocystis. They are typically unicellular or form simple filaments or colonies and inhabit freshwater habitats, sometimes moist soils and transient pools. Glaucophytes are notable for their plastids, termed cyanelles, which retain a peptidoglycan layer between the inner and outer envelope, a relic of the cyanobacterial ancestor. The cyanelles usually contain chlorophyll a and the phycobiliproteins, giving a blue-green coloration, and they generally lack chlorophyll b.

As a member of the supergroup Archaeplastida, Glaucophyta is one of the primary plastid-bearing lineages alongside Rhodophyta (red algae) and Chloroplastida (green algae and land plants). Their apparent early-diverging position in some phylogenies, and the retention of bacterial features in the plastid envelope, have made glaucophytes important for studies of plastid evolution and the origins of photosynthesis.

Ecologically, glaucophytes occur in freshwater environments worldwide, from clear streams to quiet ponds, often in nutrient-poor conditions. They contribute to primary production in their habitats and can form tiny colonies or remain solitary, depending on the species.

Despite their small diversity, glaucophytes are of considerable interest because their cyanelles preserve traits closest to the original cyanobacterial endosymbiont that gave rise to plastids, providing insight into the early evolution of plastids in eukaryotes.