No, not all aquatic plants have stomata. The presence of stomata in aquatic plants depends heavily on where the plant's leaves are located relative to the water's surface.
Stomata in Aquatic Plants: Location Matters
Stomata are tiny pores on the surface of leaves that allow for gas exchange (like carbon dioxide and oxygen). While many land plants have stomata on both the upper and lower leaf surfaces, aquatic plants show variation:
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Submerged aquatic plants: These plants typically lack stomata because they are constantly surrounded by water, making air-based gas exchange inefficient or unnecessary. They obtain the carbon dioxide they need directly from the surrounding water.
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Floating and emergent aquatic plants: These plants do possess stomata, but usually only on the upper epidermis (the top surface) of their leaves. This is because the upper surface is exposed to the air, allowing for normal gas exchange. Examples include water hyacinth, duckweed, water primrose, and bog moss. The stomata on these plants are often permanently open.
Why the Difference?
The difference in stomata presence is directly linked to the plant's adaptation to its environment. Submerged plants have evolved mechanisms for underwater gas exchange, rendering stomata unnecessary. Floating and emergent plants, however, still need air-based gas exchange and thus retain stomata on their above-water leaf surfaces.
Reference: Aquatic plants have stomata on the upper side or upper epidermis of the leaves except for submerged plants. This type of permanently opened stomata is present in floating and emergent plants like water hyacinth, duckweed, water primrose, bog moss etc.
