The same plant can have many different common names. The European white lily has at least 245, while the marsh marigold has at least 280. Clearly, if we use only the common name of a plant, we cannot be sure of understanding very much about that plant. It is for this reason that the scientific community prefers to use a more precise way of naming, or classification. 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.