Plants in the desert are very good at conserving water!
Many are known as succulents, which have fleshy leaves great for holding onto water. They also have expansive, shallow root systems that absorb water very quickly, which is important because desert rains tend to be heavy but very brief.
Additionally, many plants in the desert grown low to the ground. This is to prevent water from being lost during transport. An obvious exception is the famous saguaro cactus, which can grow to be over 70 feet tall!