The correct option is C Nerium
Generally, plants lose water via stomata due to transpiration. However, plants which grow in xeric (very dry) habitat and undergo CAM pathway of photosynthesis, have sunken type of stomata in their lower epidermis of leaves to minimize the loss of water, e.g., Nerium.
Sunken stomata refers to hidden stomata or those stomata which are not directly exposed to surface. They are present in small pits preventing the escape of water vapour from air currents which reduces water loss from the leaves.