Come off in a circle around the stem. The structure of leaves often depends on the habitat, the availability of water and the group to which they belong. These are not sharp distinctions. The outer surface of the leaf is covered by a cuticle that prevents water loss.
Cuticle is on all the aboveground green parts of plants.
The cuticle is composed of cutin, cutan, waxes. The cuticle covers the epidermis which is the outer layer of compact cells. In xerophytes the stomata may be sunken to further prevent water loss. Often you also have trichomes around the stomatal pit. There are lots of stomata on xerophyte leaves-this allows higher rates of gas exchange during periods when the water supply is favorable.