Has an extensive root system therefore can soak up a lot of water after a heavy rainfall.
Has a thick waxy skin to reduce water loss.
Has a white upper surface which reflects the suns rays.
Has spikes to protect the plant from other animals.
Plants in general
In the desert some plants do not have leaves. Instead they are replaced with spines or needles. These spines do three things:
Firstly they deter predators.
Secondly they break up the wind and insure that the cactus is always surrounded with still air.
Thirdly their small surface area reduces evaporation loss.
Desert plants often have two types of roots. Shallow ones take in any surface rainwater, and deep ones reach any type of underground water stores.
There are two types of desert plants; xerophytes and ephermals. Xerophytes have spikes and absorb large amounts after rain. Ephermals have leaves and grow after rain. The cactus is in the group xerophytes as it absorbs the rain and like ephermals does not grow after rain.
Different plants have to be adapted to their surroundings for them to survive. For example the cactus absorbs the rain with its extensive root system. If it did not have this then the 40 degree sun would dry…