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 engelmannii (state) to the Tamaulipan matorral in Chihuahua (state), in Mexico. In the Sonoran Desert, terminal pads face predominantly east-west, so as to maximize the absorption of solar radiation during summer rains. Although found occasionally in the Mojave Desert, it tends to be replaced by "Opuntia basilaris", which does not need the summer rain. The overall form of "Opuntia engelmannii" is generally shrubby, with dense clumps up to high, usually with no apparent trunk. The pads are green (rarely blue-green), obovate to round, about 15–30 cm long and 12–20 cm wide. The glochids are yellow initially, then brown with age. Spines