With regard to Mexico's native prickly pear cactus, genus Opuntia, shown at the right, both young pads -- the flat, paddle-shaped stem segments -- and the egglike fruits developing along the pads' rims, always have been eaten by Mexicans, both indigenous and mestizo. The photo shows cultivated prickly pears with immature fruits in Querétaro state. Among the many prickly pear species and varieties there are almost or entirely spineless kinds. The ones in the picture bear thorns and are grown for their fruits, called tunas. To help you enjoy Mexican mercado cactus pads and tunas, here are some terms to know

NOPAL is the de-thorned or never-thorned edible cactus. At the right you see some immature nopal pads of the kind typically sold in Mexican mercados -- with their margins trimmed away and each spine-bearing bump shaved or sliced off. Prickly pear bumps can develop two kinds of spines, the larger, easy to see ones, and much smaller, often hard to see, sharp, slender ones called glochids. If any glochids aren't conscientiously washed off, can cause considerable misery to the lips and points beyond.

NOPALITOS are small cut-up parts of nopal cactus pads often sold in mercados in pre-weighed plastic bags. If the nopalitos are chopped into smaller sections, as seen in the dish below, they're said to be picado. Nopalitos are delicious when stir-fried with onions and garlic, maybe with fresh cilantro and with eggs scrambled in, and sprinkled with lemon juice. Some regard fried nopalitos a little slimy, but the lemon juice somehow deals with that. Nopalitos often are eaten alongside a heap of refried beans and hot tortillas.

Traditional dish of nopales enjoyed in Querétaro state; copyright free image courtesy of "Pilyorlo" made available through Wikimedia Commons.

TUNAS, at least in Mexican cuisine, are the cactus fruits seen at the right. When ripe, they contain a sweet, juicy, bright-red pulp in which many small seeds are embedded. At the left, a genuine Mexican campesino shows how every day with is penknife he opens up a wild prickly pear tuna and scrapes out good stuff to eat. At the right you can barely see tufts of tiny, misery-causing spines called glochids adorn the fruit's surface. Before picking, the glochids had been brushed off vigorously by slapping with weeds with soft leaves. The the tunas were placed on the ground and brushed even more convincingly. Then they were eaten.

In mercados, where theoretically any glochids already have been removed or never had any, but still need a good washing, we find three kinds of sweet tuna -- blanca, amarilla, and encarnada (white, yellow, and red, respectively) -- and a bitter one, the xoconostle verde, for seasoning stews and salsas. The Mixtecs make a drink called nochotle of the tuna by smashing it in water, straining, and adding it to the mild, poor-man's drink called pulque.

PITAYA, shown above, is another cactus fruit, this one in the genus Hylocereus, a kind of Night-blooming Cereus growing wild on trees in Mexico's more humid parts. The fruit is sometimes called dragon fruit or strawberry pear. Inside they are white with little black seeds. One fan refers to their taste as "refreshing and palate cleansing" and says " I have cut them in half and frozen them. Makes a nice fresh substitute for sherbet in its own shell." The cactus producing the fruit has fleshy stems reaching up to 30 feet long (10m) and may climb onto walls or over trees using aerial roots. Sometimes you see pitaya plantations where supports are provided for the clambering stems to grow over.