In: Biology
The Archaeplastida (or kingdom Plantae sensu lato) are a major group of autotrophic eukaryotes, comprises of the red algae (Rhodophyta), the green algae, and the land plants, together with a small group of freshwater unicellular algae called glaucophytes.
The Archaeplastida have chloroplasts that are surrounded by two membranes, suggesting that they were acquired directly from endosymbiotic cyanobacteria. All other groups besides the amoeboid Paulinella chromatophora, have chloroplasts surrounded by three or four membranes, suggesting they were acquired secondarily from red or green algae. Unlike red and green algae, glaucophytes have never been involved in secondary endosymbiosis.