containing chlorophyll a in membrane-bound vesicles called thylakoids which are similar to the chromatophores found in photosynthetic bacteria. The thylakoids are not contained within chloroplasts. Blue-green algae also lack the large vacuoles found in the cells of plants. Possessing both chlorophyll a and b, the Prochlorophyta have a pigment system that resembles the system of land plants much more closely than does the pigment system of the blue-green algae. Thus, it has been hypothesized that the Prochlorophyta are the progenitors of the eukaryotic chloroplasts.
