It has special internal structures that absorb and hold water and a hard outer "skin" that inhibits water evaporation and transpiration from the plant. This is to take advantage of the infrequent and sparse precipitation in arid regions. That's why you'll kill a cactus if you have one as a house plant and water it every week. It will just absorb too much water and rot out from the inside. That's also why some people have been known to survive being stranded temporarily in the desert. They can cut chunks of cactus flesh and squeeze the water from it through their shirt or handkerchief and get enough water from it to drink.

Being in the desert, which is very hot, you can see why plants might have problems. But, over many, many, years, they have adapted and now they can survive under even the harshest conditions. There is little vegetation in deserts, so the animals eat what they can. Because of this the plants also need some protection against hungry animals. Plants that have adapted by changing how they look are called xerophytes. Xerophytes, such as cacti, usually have special means of storing and conserving water. They often have few or no leaves, which reduces transpiration. CACTI are the most well know Xerophytes. They have very few leaves, can store large amounts of water, and have waxy skin to conceal moisture. Also they have spines for protections against animals, to shade it from the sun and also collect moisture. Shallow roots allow large quantities of water to be collected when it rains. Because they store water in the core of stems and roots, cacti are well-suited to dry climates and can survive years of drought on the water collected from a single rainfall. Other Xerophytes include: ALOE. Its average size is 2 to 3 meters but it can reach 6 meters in exceptional circumstances. It is grown because it is decorative and for its medicinal properties. It contains a clear gel, which can be used to treat wounds and burns. It can be irritant and has spines to protect it from predators. CREOSOTE BUSH. The resin of the creosote bush protects the plant from being eaten by most mammals and insects. It is thought that the bush produces a toxic substance to keep other nearby plants from growing. Creosote bushes live for a long time, many of them living for one hundred years, and can grow about 15 feet high. Fact: There is one living creosote bush that is estimated to be nearly 12,000 years old! Another type of plant are the Phreatophytes. They have adapted by growing extremely long roots, allowing them to get hold of moisture at or near the water table. MESQUITE tree- a Screwbean Mesquite. It has very long roots which can get water even in drought periods. It also has pointy leaves to stop it getting eaten. It is good for people who have diabetes, because it controls sugar levels. Perennials are plants which appear to have died, but as soon as water becomes available, the come springing back to life. The OCTILLIO is an, funnel-shaped desert plant with several, spiny, whip-like, straight branches, which helps protect itself from animals. The branches can be rising as high as 20 feet. Ocotillo are leafless most of the year, except immediately after rain; the leaves then quickly die after the soil dries out. The leaves are about 2 inches long, appearing in bunches above spines. Annuals are plants that live for only a season- when the rain comes. DESERT PAINTBRUSH, is but one of a large, easily recognizable, early bloomer. It grows 4 to 16 inches high and has leaves that are 1 to 2 inches long, the top being divided into as many as 5 narrow lobes. DESERT SAND VERBENA are sticky, hairy creepers that have flower stalks up to 10 inches long, with stems trailing up to 3 feet. Sand Verbena can carpet a desert for miles after lots of winter rain. Other- The WELWICHIA. It has only two leaves, and is very, very big. It is about 2 meters high, and takes up about 16 square meters. It can live for very long, and the longest living one at the moment is about 200yars ond. UMBRELLA THORN ACACIA. It has thorn branches about 15 meters spread out and they are flat along the bottom. Its thorns are curved or straight- but the seed pods are long and twisted. The flowers are creamy white, and are perfect food for giraffes, elephants and monkeys. Hope it helps =)