A Single-celled Imposter

Having discussed the characteristics of cells at some length, to mention Caulerpa floridana (“turtle grass”) may seem to undo it all. Here is an organism that seems to have leaves, stem, and roots (or rhizoids); an organism that can reach a length of two feet or more. Yet it is a single cell! Although it contains great numbers of nuclei, mitochondria, and chloroplasts, it has no cross walls, and, hence, is not divided into a number of cells. This puts Caulerpa in the kingdom Protista; and to be faithful to the concept of five kingdoms, it is not a plant.