A2A. Some do but I faintly remember my old plant biology professor saying that stomata are placed on the underside as to not lose moisture. This also explains why a lot more are open during nighttime when the temperature is lower and you lose less moisture through evaporation. read more
In dorsiventral leaves, stomata are located on the lower surface (lower epidermis) to reduce the transpiration. If stomata were on thw upper epidermis, rate of transpiration would have been much higher, thereby causing damage to the plant. read more
In most green plants, the stomata are located on the lower side of the leaves. According to biologists at Colby College the leaf of the water lily has about 460 stomata per square millimeter on the upper surface of their leaves while many other plants, like the garden lily, have none at all. read more