I joined APLD folks to talk to people about CA native plants at the California Academy of Sciences. I like to do this sort of thing.
Here are some of the characteristics of native plants that help them conserve water:
Slivery grey leaves with little hairs reflect light help keep a plants temperature down in hot dry climates.
Small leaves help plants conserve water because less surface area means that leaf will lose less water.
Waxy leaves serve as sort of a waterproofing that reduces transpiration.
Thick succulent leaves trap and conserve water.