Hydrophytes, or aquatic plants, possess stomata primarily to facilitate transpiration and gas exchange in those that float on the water's surface.
Understanding Hydrophytes and Stomata
Hydrophytes are plants adapted to living in aquatic environments. They are categorized into three main types:
- Submerged hydrophytes: These plants are entirely underwater (e.g., Hydrilla).
- Floating hydrophytes: These plants have leaves that float on the water surface (e.g., Water Lily).
- Amphibious hydrophytes: These plants can survive in both aquatic and terrestrial environments (e.g., Sagittaria).
Stomata are small pores on the epidermis of leaves and stems that regulate gas exchange (carbon dioxide intake and oxygen release) and transpiration (water vapor release).
Stomata in Floating Hydrophytes
Floating hydrophytes have stomata on their upper leaf surfaces for the following reasons:
- Transpiration: Stomata enable transpiration, which helps in regulating the plant's temperature and facilitating the upward movement of water and nutrients from the roots. Although surrounded by water, these plants still need to control water loss.
- Gas Exchange: Stomata allow the intake of carbon dioxide from the atmosphere for photosynthesis and the release of oxygen as a byproduct. Since the lower surface is in contact with water, gas exchange is primarily limited to the upper surface. The upper epidermal cells of hydrophytes are also often specialized to prevent water from clogging the stomata.
Stomata in Submerged Hydrophytes
Submerged hydrophytes generally lack stomata. They absorb water, nutrients, and gases directly from the surrounding water through their cell walls. Since they are completely submerged, stomata would be non-functional.
Adaptations of Hydrophytes
Hydrophytes exhibit several adaptations related to their aquatic environment, including:
- Reduced root systems: Submerged plants can absorb nutrients directly from the water.
- Air spaces (aerenchyma): These spaces in the stems and petioles provide buoyancy and facilitate gas exchange.
- Thin cuticles: A thin or absent cuticle allows for the direct absorption of water and nutrients in submerged plants.
- Flexible stems: To withstand water currents.
In summary, while some hydrophytes, especially submerged ones, lack stomata, floating hydrophytes possess them primarily on the upper leaf surface to facilitate transpiration and gas exchange essential for their survival.
