Opuntia ficus-indica a fruit crop, and also for the vegetable nopales and other uses. Most culinary references to the "prickly pear" are referring to this species. The name "tuna" is also used for the fruit of this cactus, and for "Opuntia" in general; according to Alexander von Humboldt, it was a word of Taino origin taken into the Spanish language around 1500. Cacti are good crops for dry areas because they convert water into biomass efficiently. "O. ficus-indica", as the most widespread of the long-domesticated cactuses, is as economically important as maize and blue agave in Mexico. Because "Opuntia" species hybridize easily,
Opuntia arenaria Opuntia arenaria Opuntia arenaria was considered a variety of "O. polyacantha" by many botanists, and is still treated that way in the Flora of North America. However, "O. arenaria" is diploid and "O. polyacantha" is tetraploid. It was described by Engelmann in 1856. "Opuntia arenaria" can grow in soil that is essentially pure sand. It has rhizomes up to 1.5 m long that give rise to above ground shoots with small cladodes that are 4-7 x 2–3 cm in size. Major spines are found in the distal areoles and are often reflexed, up to 30 mm long. Minor spines are