It has small linear leaves as there is no competition for sunlight, and it loses less water (which is scarce in hot deserts), as the less surface area it has, the less evapo-transpiration occurs. They are also hairy and slightly succulent, meaning that they can store water.
Great Basin Sagebrush
It has tap roots up to 25m long, giving it a larger surface area to absorb water, and needle-like leaves, to reduce water-loss from evapo-transpiration.
Giant Saguaro Cactus
The cactus is succulent, so it stores water, with roots very close to the surface so it can soak up water before it evaporates. Its skin is pleated so the cactus can expand when it soaks up water. It has needles to protect itself from animals that might eat it.
Joshua Tree
It has needle-like leaves to minimise water loss and protect itself from animals trying to eat it. The tree's leaves are coated with a waxy resin which minimises water loss, and tastes horrible to animals trying to eat it.