The Cynobacterium That Could
Eye candy and science in this article about leaves at National Geographic.
"[Leaves] evolved about 1.6 billion years ago when one cell, incapable of using the sun’s energy, engulfed another cell—a cyanobacterium—that could. That cyanobacterium became the ancestor of every living chloroplast. Without their chloroplasts plants would be left like the rest of us, to eat what they find. "