Answer:
The correct answer is - cyanobacterium.
Explanation:
According to the endosymbiotic theory eukaryotic cells are rise through the engulfing the endosymbiotic cyanobacteria by prokaryotic cells and from cells with specialized cell structure like chloroplast and mitochondria.
Archaeplastida are all the plant kingdom with red green algae and land plants included in this group are descended from heterotropic protist by the process of engulfed an cyanobacteria.
Thus, the correct answer - cyanobacteria.
