What is a leaf called that has stomata only on its upper surface?

Phyllode of $Acacia$ $auriculiformis$ is considered a leaf modification because:

Example of a leaf modified for climbing.

Stomata in grass leaf are

Axillary bud and stipules are absent in

You have heard about several insectivorous plants that feed on insects. Nepenthes or the pitcher plant is one such example,which usually grows in shallow water or in marshy lands. What part of the plant is modified into a pitcher? How does this modification help the plant for food even though it can photosynthesize like any other green plant?