Cactus

CACTUS. Cacti are succulent perennials that are native to arid and semi-arid regions and are cultivated extensively, except where freezes regularly occur. The land area devoted to cactus cultivation in 2001 was about 1.8 million hectares (4.4 million acres), mostly for fodder, and over half of which was in northern Africa and northeastern Brazil. Cacti are also cultivated in over twenty countries for their fruits, which commercially fall into three categories: cactus pears, which are the fruits of the prickly pear Opuntia ficus-indica and certain other cacti with flat stems (cladodes), and represent over 90% of the cactus fruits sold; pitahayas, which are the fruits of vine cacti in the genera Hylocereus and Selenicereus; and pitayas, which are the fruits of columnar cacti. Young cladodes are consumed as a vegetable (nopalitos), particularly in Mexico. Nearly all cacti employ a photosynthetic pathway known as Crassulacean acid metabolism (CAM), in which the stomates (shoot pores that allow CO₂ entry) open primarily at night, when temperatures are lower and water loss is lower than for the overwhelming majority of plants, whose stomates open during the daytime. The best known edible CAM plant is pineapple, which is cultivated on about half as much area as cacti. Because of their lower water loss, cacti and other CAM plants thrive in dry regions (and also require little or no irrigation when cultivated in other regions.

History

Although evidence for cacti in human diets goes back more than 8,000 years in present-day Mexico, worldwide consumption has developed only in the last few hundred years. Cacti were introduced into Europe in 1495 from the second trip of Christopher Columbus to the New World. Opuntia ficus-indica spread across the Mediterranean region in the sixteenth century, where it readily grew under the local semi-arid conditions. Also in the sixteenth century, Spaniards introduced Hylocereus undatus into the Philippines, whence it spread throughout southeast Asia. In the nineteenth century, it became established in Viet Nam and is now extensively cultivated in the Mekong Delta, where its tasty fruit with red peel and white pulp is called "dragon fruit." Also in the nineteenth century, the columnar Stenocereus queretaroensis was domesticated in Jalisco, Mexico. None of these species received much agronomic attention until the end of the twentieth century, and even then the money for research and development was meager. Both fruit crops and young cladodes used as vegetables require much hand labor. Although machines have been developed to remove the irritating small spines (termed "glochids") from cactus pears, many improvements in their cultivation await future research.

Fruits

Fruits of many cacti are edible. Indeed, the Seri Indians of the southwestern United States and northwestern Mexico consumed fruits from over twenty species, including those of the saguaro cactus (Carnegiea gigantea), used by various Native Americans for fruits and wine. Fruits collected from the wild influenced the species selected for domestication. Such selections involved various species of Opuntia in Mexico, eventually leading to the presently planted cultivars.

Cactus pear. The fruits of Opuntia ficus-indica and a few other prickly pears are harvested in the summer from plants that are one to three meters tall. Harvest can be delayed by removing the early flowers, as is commonly done in Sicily, leading to a second harvest in the autumn that is more valuable per fruit due to lessened competition from other species. One-year-old cladodes can bear five to fifteen fruits each; terminal cladodes with fewer fruits tend to bear larger ones (over 150 g each), which command higher prices. After harvesting, the fruits must have the glochids removed mechanically, after which they are often packaged by color and weight. Fruits with red pulp are prized in the United States and certain European countries, whereas greenish pulp for mature fruits is generally preferred in Mexico. Although sold in supermarkets worldwide, fruits are also sold by street vendors, who slice the peel and provide the exposed pulp directly to the consumer. The relatively large seeds are a detriment to fruit consumption by many, but the seeds are harmless and readily swallowed by aficionados.

The country with the greatest land area devoted to cactus pear cultivation is Mexico (Table 1). Annual production can be over fifteen tons fresh weight per hectare under intensive management. In Mexico, Sicily, Israel, and the United States, most production is from commercial plantations, whereas in other Latin American countries and in northern Africa, a large amount of the fruit is collected from hedges and other informal plantings.

Pitahayas and pitayas. The most widely cultivated pitahaya is Hylocereus undatus, which in 2001 was cultivated on about 12,000 hectares in many countries, including Viet Nam, Taiwan, the Philippines, Mexico, Guatemala,

Peru, Colombia, and Israel. It is a vine that is trained to grow on posts, trellises, or arbors. Its relatively large fruits (generally 250 to 500 g) are harvested after the peel, which has no spines or glochids, turns red. The pulp is

Vendor selling cactus pads in Guanajuato, Mexico. © DANNY LEHMAN/CORBIS.

whitish with small black seeds. Other species of Hylocereus and Selenicereus megalanthus have peels and pulps of various colors, leading to a wide choice of tasty and visually appealing fruits.

Although their cultivation is expanding rapidly, in 2001 pitayas were harvested on only about 3,000 hectares worldwide, mostly in Mexico, from species like Cereus peruvianus, and especially Stenocereus queretaroensis and other Stenocereus species. Fruits grow along the main stem and branches about two to six meters above the ground, requiring a pole with a basket-like attachment for harvest of individual fruits. Fruits of Stenocereus queretaroensis have an attractive and tasty dark red or purple pulp with small seeds (like those in kiwis) that are easily swallowed. However, the fruits tend to split within two or three days after harvest, requiring rapid local consumption.

Vegetables

Tender young cladodes about 10 to 15 cm long of Opuntia ficus-indica, Opuntia robusta, and a few related species are used in Mexico as nopalitos. About 6,000 hectares were cultivated for this purpose in 2001, and nopalitos are also prepared from plants in the wild or growing around houses, or as hedges. The raised portions of the stem containing spines and glochids are readily removed with a knife or by machine. The cladodes are then generally sliced or diced and blanched in a weak saline solution for a few minutes to remove excess mucilage. After draining, the material can be cooked, yielding a vegetable with a taste not unlike string beans or okra. Because of their high fructose and mucilage content, nopalitos are highly recommended for people with type II diabetes. Often the blanched material is pickled and used as a relish or in salads. More than thirty companies sold pickled nopalitos in Mexico in 2001, and this product is in supermarkets worldwide.

Other Uses

Other uses of cacti range from candy made from the stems of barrel cacti that have been infused with a sugar solution to peyote from dried stems of Lophophora williamsii, used by Native Americans for ceremonial purposes. Flowers have been used for medicinal purposes and to make perfume. The seeds of cacti such as Opuntia ficus-indica have been dried, ground, and then used as a flavoring paste for cooking. Carminic acid, an important red dye for food coloring, can be extracted from dried cochineal insects that feed on Opuntia ficus-indica. Although most cactus pears are consumed fresh, sorbets and marmalades are also prepared from the fruits. The strained pulp of fresh fruits is used as a fruit drink or fermented to make wine. Fruits of cactus pears are also partially dried and sold in brick-sized blocks in Mexico. More than thirty brands of dried and powdered cladodes are sold in Mexico as a dietary supplement. The range of edible products from cacti is indeed great and their use is steadily increasing, as more people become willing to try new and natural foods, and growers search for crops that do not need irrigation.

Park S. Nobel