Relationship to chloroplasts
Chloroplasts found in eukaryotes (algae and plants) appear to have evolved from an endosymbiotic relation with Cyanobacteria. This endosymbiotic theory is supported by various structural and genetic similarities. Primary chloroplasts are found among the "true plants" or green plants – species ranging from sea lettuce toevergreens and flowers that contain chlorophyll b – as well as among the red algaeand glaucophytes, marine species that contain phycobilins. It now appears that these chloroplasts probably had a single origin, in an ancestor of the clade calledArchaeplastida, yet this does not necessitate origin from cyanobacteria themselves, microbiology is still undergoing profound classification changes and entire domains (such as Archaea) are poorly mapped and understood. Other algae likely took their chloroplasts from these forms by secondary endosymbiosis or ingestion.