Solution

Sunken stomata lie in pits or depressions (stomatal crypts) lined with hairs. They reduce water loss by keeping a layer of moist air over the stoma.
They are a xerophytic adaptation, found in Nerium (oleander), Pinus and Cycas. In Nerium the leaf has multiple epidermis and sunken stomata in crypts.
Hydrilla is a submerged hydrophyte with no functional stomata; mango and guava are mesophytes.
So sunken stomata are found in Nerium.

Concept Sunken stomata in Nerium

Anatomy of Flowering Plants in past papers

86 questions from this chapter have appeared across 26 exam years.