Duke University Botany Dept.
Green plants encompass both land plants and green algae.
The streptophytes encompass land plants and closely related green algae known as charophytes, while the chlorophytes include the rest of the green algae. Until now, no green algae were known that predated the evolutionary divergence of green plants into two distinct evolutionary lineages, and since the earliest diverging green algae show considerable morphological variation, the nature of the unicellular ancestor of green plants was unknown. It is generally accepted that chloroplasts are derived from cyanobacterium which took up residence within non-photosynthetic eukaryotic cells, establishing an endosymbiotic relationship whereby the eukaryotic cell provided a new niche for the bacterium, and the bacterium provided photosynthetic energy for the eukaryotic cell. Over time, the cyanobacterium evolved into a chloroplast within the host cell, giving rise to the first red algae. By comparing the protein sequences of 53 genes common to M. viride , three land plants, three members of the Chlorophyta, the glaucocystophyte Cyanophora paradoxa , the red alga Porphyra purpurea and the cyanobacterium Synechocystis sp.