In Mexico there are between 66 and 97 species of Opuntia, divided into 17 series. One of these series is the Tunae, which consist of low shrubs with cladodes that detach from the plant, though not easily, and have a pubescent epidermis. In the dry season the areoles are sometimes surrounded by a purple spot. The cladodes have acicular, subulate, yellow or white spines. The fruit is red and fleshy. During the exploration in the Sierra of Abra Tanchipa Biosphere Reserve, situated in the first foothills of the Sierra Madre Oriental, East of the state of San Luis Potosí, a cactus pear was discovered. This cactus pear cannot be classified among the known species of Opuntia due to its distinct morphological characteristics. However, it does possess features typical of the members of the Tunae section. Therefore, it is proposed as a new species within this series, named Opuntia fortanelli. The differences between O. fortanelli, the proposed species, and the closely related species O. decumbens and O. elizondoana, are discussed.