VEGETATION IN DESERTS
Life in the desert is difficult for plants, since they cannot run and hide in the shade or bury themselves underground like animals. The Sun scorches, and temperatures change from infernal heat during the day to very cold nights. Also, rain is extremely scarce, and when it does come it is always violent and torrential.
In order to survive, desert plants have learnt to be resistant, to wait, and to grow and reproduce quickly when rain does fall. Despite these limitations, desert vegetation is low and sparse. In general, the plants have a dry, spiny look, and trees are very rare indeed (most of them belong to the acacia family).
To endure the driest season, desert plants use three clever tricks: (1) some plants lose their stems and leaves and survive solely through their roots, (2) other plants wither and leave their seeds waiting for the next rainfall, and (3) the true desert plants-the only ones that are permanently visible-have gone through great transformations in order to be able to conserve water the cacti are the most well known of these).
In order to avoid having to share water with other plants, many species have developed toxic mechanisms to repel neighbors and fellow species and keep them off their territory. the result is that the plants stay very away from each other.
Source: Llamas, Andreu, "The incredible world of plants; plants of the deserts|", Chelsea House Publishers, New York, 1996. pp. 6-7.