Over half of Mexico’s land is classified as arid. Another 30% of the land is classified as semi-arid. The only true dessert (where the annual rainfal is less than 25 cm or 10 inches) is the Desierto de Altar in northwest Sonora. The northwest Mexico is much covered with the dry scrublands (Chihuahua, Sonora and Baja California). Desserts and scrublands conceal a surprising abundance of wildlife.
Cactuses have adopted to the harsh conditions of life in desserts. Northern Mexico are characterized by the extraordinary variety of cactuses that grow there. 300 spices of cactus exist in this part of the world.They are superbly adapted to retain water. Cactuses withstend fierce climatic extremas. Their fleshy stems often protected by spines are filled with water-storing tissue. Cactuses are surrounded by a thick , waxy lawyer to help retain moisture. Cactuses remain dormant for long periods. Then burst into bloom after a brief downpour. Cactuses are used for drink and food, also for roof coverings. Also, cactuses are used to make fish hooks and pot scourers in Mexico.
Prickly pears (Opuntia species)-the large cactus group, are also called Indian figs. Many have edible red, green or purple fruits.
The giant Mexican cereus (Pachycereus pringlei)-is a tall, treelike cactus. They are often planted close together in rows to form fences.
The barrel cactus ( Ferocactus)- derives its name from its rounded shape. Mexico has nine species of barrel cactus.
The saguaro ( Carnegiea gigantea)- can grow to 16 m (52 ft) tall, taking nearly 150 years to reach its full height. Large specimens can hold several tons of water.
The boojum tree (Idria columnaris)- is an extraordinary sight. It is seen mainly in the dessert of Baia California.
Agave-are used to make tequilla and henequen. Some species take up to 50 years to flower.
Most cactuses store water in fleshy stems. But many other succulents such as the agaves, store moisture in their leaves. Succulents grow very slowly to reduce their need for water. Many have shallow, but very extensive, root systems.