Botanists name a plant to give it a unique place in the biological world, as well as to clarify its relationships within that world. Classification is sometimes difficult. As modern botany has advanced, producing an increasing understanding of complex biochemical mechanisms, the criteria for the way plants are classified has undergone transformation. Even further, Nature is not fixed and plants, like us, are capable of change. Plants can vary for reasons we don't entirely understand.
Science classifies living things in an orderly system through which they can be readily identified.
Living things are grouped into categories of increasing size, based upon relationships within those categories. For example, all plants can be put in order from the more primitive to the more advanced. Small with leaflike, stemlike, and rootlike structures. Larger with true leaves, stems, and roots. Ferns, horsetails, club mosses.