Plants in hot, dry places such as deserts lose water quickly and have little water to replace it. Plants adapted to these conditions are called xerophytes. Most of the water a plant loses leaves through the stomata in transpiration, so their adaptations reduce the rate of transpiration.
Leaf size and shape matter. Small, narrow or needle-shaped leaves, or leaves reduced to spines, have a small surface area, so less water can evaporate from them. Some plants roll their leaves, and many have hairs. Both trap a layer of humid air next to the stomata. This lowers the concentration gradient of water vapour between the leaf and the air, so transpiration slows.
The cuticle is the waxy, waterproof layer on the leaf surface. In desert plants it is thicker, so less water escapes through the surface of the leaf. Stomata are the pores that let water vapour out and carbon dioxide in. Desert plants often have fewer stomata, or stomata sunk in pits where humid air collects, and some keep them closed during the hot day. The cost is that less carbon dioxide can enter, so photosynthesis is slower.
Cold regions are also hard places to live because water in frozen ground cannot be taken up by roots. Conifers have narrow, needle-shaped leaves with a thick cuticle, which helps them conserve water.