Which of the following is the only taxonomic categories that has a real existence?

Species is the lowest or basic taxonomic category which consists of one or more natural populations of individuals that resemble one another more closely than individuals of other species, interbreed freely, have a distinct genetic set up and are reproductively isolated from others e.g., Panthera Leo (Lion), Mangifera indica (Mango), Solanum tuberosum (Potato).