Biologists have found in plants a useful gene to differentiate species: it varies from one species to another, but not from one grain to another. This means that they only have to study this gene to know which species a plant belongs to. It is especially useful for differentiating apparently equal species from each other. It is a chloroplasts gene, called matK, which means that it moves, but not as fast as those of the nucleus, but as fast as to change throughout the process of creating new species. Biologists do not believe that all existing plant species can be separated thanks to the matK gene, but most do.