HYDROPHYTES (WATER PLANTS)
What is hydrophytes (water plants)? Water plants are submerged, emergent or floating.
- The leaves have an epidermis with very thin walls and a delicate cuticle.
- They have no stomata.
- Water is excreted from special glands and pores at the tips.
- Other adaptations include the following:
- Presence of large air spaces and canals (aerenchyma) for gaseous exchange and buoyancy.
- Some plants have filamentous leaves In order to increase the surface area for absorption of light, gases and mineral salts.
- Some plants are rootless, hence support provided by water.
- Mineral salts and water absorbed by all plant surfaces.
- In some plants, the stem and leaves are covered with a waxy substance to reduce absorption of water. e.g. Ceratophyllum and Elodea sp.
Their structure is similar to that of mesophytes. The leaves are broad to increase the surface area for water loss. They have more stomata on the upper surface than on the lower surface to increase rate of water loss. Examples are Pistia sp. (water lettuce), Salvinia and Nymphea.
Halophytes (Salt plants)
- These are plants that grow in salt marshes and on coastlines.
- They have root cells that concentrate salts and enable them to take in water by osmosis.
- They have salt glands which excrete salts.
- Fruits have large aerenchymatous tissues for air storage that makes them float.
- Some have shiny leaves to reduce water loss.
- The mangrove plants have roots that spread horizontally, and send some branches into the air.
- These aerial roots are known as breathing roots or pneumatophores.
- They have lenticel-Iike openings called pneumatothodes through which gaseous exchange takes place.