A sunken stomata is a stomata in a small pit, which protects the escaping water vapor from air currents, decreasing water loss from the leaf. Sunken stomata are commonly found in plants in arid environments as one of their adaptations to preserve water. Plants with sunken stomata often have fewer stomata in general than plants in moister environments.
Sunken stomata are a feature of many plants in deserts and other dry environments. Stomata are tiny holes, generally on the bottom surfaces of leaves, that allow for gas exchange and the release of water vapor. In moist environments, this is often necessary because the plants take in more water than is necessary for photosynthesis. It is not necessary in deserts, but because of the need for stomata for gas exchange, plants in dry environments cannot prevent some water loss. They minimize this loss through structures like sunken stomata.
Other plant adaptations to life in dry environments include waxy cuticles, rolled leaves and small needle-like leaves. Waxy cuticles both prevent water loss directly and reflect heat, a major cause of water loss through evaporation. Rolled leaves keep their stomata inside, slowing water loss in the same way as sunken stomata. Needle-like leaves both reduce surface area and, in the case of some plants, act as a defense against herbivores.