In the desert areas, which have less moisture, Xerophytic plants, which adapt in dry conditions, grow. The largest plant of this variety are the cacti, found in the tropical regions of America, Africa and Madagascar.
Since, such plants have no leaves, the extent of transpiration is very less. Chlorophyll function occurs thought the trunks, which are green due to the presence of chlorophyll in the epidermis. They are cylindrical in shape and able to collect water whenever it rains.
Below Cacti info from Wikipedia (Read More):-
A cactus (plural: cacti') is any member of the plant family Cactaceae, native to the Americas. They are often used as ornamental plants, but some are also crop plants. Cacti are grown for protection of property from wild animals, as well as many other uses. Cacti are part of the plant order Caryophyllales, which also includes members like beets, gypsophila, spinach, amaranth, tumbleweeds, carnations, rhubarb, buckwheat, plumbago, bougainvillea, chickweed and knotgrass.
Cacti are distinctive and unusual plants, which are adapted to extremely arid and hot environments, showing a wide range of anatomical and physiological features which conserve water. Their stems have adapted to become photosynthetic and succulent, while the leaves have become the spines for which cacti are well known.
http://en.wikipedia.org/wiki/Cacti
