Iuncusaquatilis immaturus
This is the first true plant. It anchors itself on the ocean floor and just sits and photosynthesizes. The cells of this organism have specialized into three distinct types. The outer cells are the ones that use the light and turn it into food. The inner cells carry the food so it can reach every cell in the organism. The bottom cells are what allow it to stick to the ocean floor and have a limited photosynthesizing ability. When it reproduces, one of the bottom cells will split and float off. When it lands, it will grow a new Iuncusaquatilis immaturus. At this time, it is the largest single living organism.