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 readily between species. This can make classification difficult, yielding a reticulate phylogeny where different species come together in hybridization. Also, not all species listed here may actually belong in this genus, meaning that "Opuntia" is not a monophyletic group. "Opuntia" also has a tendency for polyploidy. The ancestral diploid state was 2n=22, but many species are hexaploid (6n = 66) or octaploid (8n = 88). Chollas, now recognized to belong to the distinct genus "Cylindropuntia", are distinguished by having cylindrical, rather than flattened, stem segments with large barbed spines. The stem joints of several species, notably the jumping cholla ("Cylindropuntia