If there is not enough water, leaves close their stomates and wilt to control water loss. Wilting is a sign that the plant is in trouble. Waxes and hairs on the leaf keep it from drying out. Some hairs may have glands on them or have a star-shaped top. Some hairs may function to control insect damage.
Leaves come in many shapes and sizes.
This is often how we identify the plants. You may find two leaf shapes on one plant. Evergreen plants have leaves all the time, but not the same set of leaves. They put on a new set of leaves and lose the old. For instance, magnolias go through this transition in spring.