The red and green algae are descendents of the primary endosymbiosis event that resulted in the first chloroplast. Their plastids have two membranes, an inner membrane that was the cyanobacterial cell wall and an outer membrane from the organism that first engulfed it. The story of these algal groups is the evolutionary history of all plants. As time passes in this story and groups specialize for their given environments, we will see changes in cell wall composition, photosynthetic pigments, storage carbohydrates, and life cycles. Make note of these important differences between groups, as they represent the primary ways we classify these organisms.