RANK Everyone realizes that some plants are more alike than others. I suspect that most of you can distinguish a pine from other conifers. This statement implies that you can recognize two levels of grouping - one that consists of different kinds of pine and then a more inclusive group, conifers, that includes pines plus many other kinds of conifer. One way to recognize such differences in degrees of similarity is to recognize groups as having different ranks. The highest rank recognized nowadays is the Domain .
Plants belong to the Eukaryote Domain, as do humans.
Below this comes the kingdom. Humans belong to the kingdom of animals. The kingdom of plants is now restricted to such things as flowering plants, gymnosperms, mosses, liverworts, and green algae. It used to include fungi and all the algae. There are then additional ranks until one gets to the lowest formal rank, one that is rarely ever used but is theoretically possible, a subform.