glaucophyten

Glaucophytes, or the division Glaucophyta, are a small group of microscopic freshwater algae that occupy a basal position within the Archaeplastida, the supergroup that also includes red algae, green algae, and land plants. They are among the earliest diverging photosynthetic eukaryotes and are valued for retaining ancestral traits of plastids. The division comprises a limited number of described species, found primarily in freshwater habitats and, less commonly, in damp terrestrial environments.

A hallmark of glaucophytes is their plastid, known as a cyanelle. Cyanelles resemble a reduced chloroplast and are characterized by a persistent peptidoglycan layer between their inner and outer membranes, a feature inherited from the cyanobacterial ancestor of plastids. Glaucophytes contain chlorophyll a and the phycobiliproteins (such as phycocyanin and phycoerythrin), which give their cells a bluish-green tint. They have a simple cellular organization, typically a single cyanelle per cell, and often store starch as an energy reserve. Their cell walls commonly contain cellulose.

In terms of life cycle and reproduction, glaucophytes reproduce primarily by asexual division, though the details can vary among species. Sexual reproduction has been little observed and remains poorly understood in many cases. They are generally photoautotrophic and rely on light for energy, inhabiting freshwater environments where they contribute to microbial communities and primary production.

Taxonomically, Glaucophyta is a distinct but modestly sized lineage. The best-known model species is Cyanophora paradoxa, which has been studied for insights into plastid evolution. Glaucophytes provide key evidence for the origin of plastids through primary endosymbiosis and help illuminate the early steps in the evolution of photosynthetic eukaryotes.