When we think about the evolution of life on our planet, we usually think of minuscule single-celled organisms as the simple precursors to more complex, multi-cellular life forms.
You might remember seeing single-cell organisms under a microscope in biology class, and perhaps you remember them as rather boring blobs. Life got much more interesting and complex when the cells joined together to become animals or plants. Most people, biologists as well as you and I, think of cells primarily as building blocks of more complicated organisms.
That's why an organism called Caulerpa, a kind of alga, is so fascinating. There are over 70 different species of Caulerpa, which grow in warm, shallow lagoons around the world. If you saw one of these growing on the sea floor, you would think it was an aqueous plant, no different from any other type of seaweed. You would be wrong. Although Caulerpa has a complex structure with parts that look like leaves and stems and roots, and although it can grow to be over three feet long, it is actually a single cell.
Caulerpa has only a single cell wall, surrounding the whole organism from the root tips to leaves. Within, the liquid of the cell flows freely. Structural support comes from a series of microscopic rods and microtubules, taking over the function of cell walls in multi-cellular plants.
Perhaps the most interesting thing about Caulerpa is what it teaches us about life and evolution. It shows us that complex life does not need to evolve along only the lines we expect. Life can often surprise us!