During a walk around a pond or a lake, the water lilies with their eye-catching and large flowers have certainly caught your eye. They are probably the best known hydrophytes (aquatic plants) and thus well adapted to life in the water.
hydrophytes, also called aquatic plants, are all higher plants that grow completely or partially in water. Here you can distinguish between water swimmers and water roots.
Hydrophyte locations
Aquatic plants, as the name suggests, are mainly found in permanently wet areas. This is often the case Sweet-, brackish– or seawater without strong currents. In addition, hydrophytes can also be found on riparian and swampy areas where they are only temporarily submerged.
Brackish water is sea or sea water with a salt content of 0.1% to 3%. Water with a lower salinity is called fresh water.
Hydrophytes – Classification
All hydrophytes belong to the macrophytes. These are plants that are visible to the naked eye. In the case of aquatic plants, this term is often used to distinguish them from the microphytes to distinguish, to which among other things the algae belong.
at macrophytes are plants that are visible to the naked eye as individuals. microphytes on the other hand, are plants that are so small that you cannot see them as a single plant with the naked eye.
pleustophytes
pleustophytes are hydrophytes that float freely on water and are not anchored to the bottom. In still waters they form blankets floating on the water surface.
pleustophytes, are also called floating plants or water floaters and are a subspecies of hydrophytes that float freely on the water. Water swimmers can be found in still, nutrient-rich waters, because otherwise they would drift away too quickly due to their lack of anchoring in the ground.
The roots do not reach down to the bottom of the water, but are often greatly reduced and therefore only serve to absorb nutrients from the surrounding water. Their leaves and flowers float on the water and are thus in constant exchange with the air. Well-known examples of the pleustophytes are the water hyacinth, the floating fern and the duckweed.
rhizophytes
rhizophytes describes plants that have roots. With regard to aquatic plants, one can distinguish between pleustophytes and water roots.
The rhizophytes are also referred to as the actual hydrophytes because they are anchored to the bottom of the water with the help of their roots. Here you can distinguish between submerged (submersed) rhizophytes and the floating leaf plantssome of which also grow above water.
Submerged rhizophytes
The submerged rhizophytes are hydrophytes that grow completely under the water surface. They are often found in nutrient-rich, eutrophic Find lakes in which they have their own zone that dive sheet zone, form. This zone is located in the littoral of the lake between the floating leaf zone and the deep algal zone.
A body of water is called eutrophic referred to when it has a high nutrient content and the water therefore appears very cloudy and greenish. Here will be more biomass, i.e. organic matter such as plants and dead organisms, is produced than can actually be broken down. This also results in a low oxygen concentration.
If you would like to know more about eutrophication, please have a look at the relevant article on .
If you want to know more about the different zones of a lake, please have a look at the article “Lake Structure” or “Litoral”.
floating leaf plants
The floating leaf plants usually have large leaves and flowers that float on the water surface. They are anchored to the bottom of the water with their roots. The floating leaf plants form their own zone in the lake as well floating leaf zone referred to as. This is located between the diving sheet zone and the reed zone.
littoral helophytes
Both littoral helophytes These are bank plants that are only temporarily under water, depending on the water level of the water body. That’s why you can also use them as amphiphytes describe. This means they are intermediate between the helophytes and the hydrophytes.
helophytes are marsh plants that occur in damp to wet and partially flooded locations.
Hydrophytes – structure
In contrast to land plants, the plant parts of the hydrophytes sometimes have other functions that are based on life under water. However, the basic structure is similar.
root
In contrast to land plants, the roots play a rather subordinate role for hydrophytes. For some species they are important for anchoring to the bottom of the water, but the floating leaf plants only take up nutrients with their roots. Since the roots of aquatic plants are not used to absorb water, as is the case with terrestrial plants, they are often reduced to such an extent that no nutrients can be absorbed. The leaves then take over this task.
leaves
Aquatic plants often have two different types of leaves, located below and above the water. The underwater leaves are often reduced and have none cuticlebecause here no perspiration protection is necessary. The leaves above the water surface are thin and slit to allow optimal gas exchange with the surrounding air. Gas exchange is particularly important for aquatic plants because this can only happen in the air, i.e. on a small area of the plant.
The cuticle is a layer of wax found on the epidermis, which is the outermost layer of the leaves. Thus, the cuticle is the final layer to the environment and protects the leaf from possible water loss through evaporation, which is also called transpiration.
sheet cross section
The floating blades differ from the underwater blades and therefore also in the blade cross-section. A cuticle is usually only present in floating leaves, because only these can carry out a gas exchange with the air. Thus, only the floating leaves have guard cells on the upper side of the leaf.
The necessary carbon dioxide for photosynthesis can be absorbed here. That is particularly important aerenchyma, which is a tissue in which air is stored and thus provides buoyancy for the leaves. In addition, the oxygen supply in plant parts lying under the water surface can also be guaranteed in this way.
That aerenchyma is a so-called ventilation fabric that has large intercellular spaces in which air is stored. In aquatic plants, the aeration tissue is important for the gas exchange of the submerged parts of the plant.
palisade fabric
Often only the floating leaves have palisade tissue, because this is where the chloroplasts are located. However, here too the separation between the palisade tissue and the spongy tissue is not very clear because the cells are loosely arranged.
The palisade tissue is the layer in leaf cross-section that lies between the epidermis and the spongy tissue. It is rich in chloroplasts and thus mainly responsible for photosynthesis. Depending on the position of the leaf on the plant, the palisade tissue is more or less pronounced.
scion
Like the leaves, the stem axis of hydrophytes contains an aerenchymal tissue that is responsible for gas exchange. These air channels allow gas exchange with submerged plant parts, including carbon dioxide, which is essential for photosynthesis.
Hydrophytes – Adaptations and Peculiarities
Living on or under the water requires some adaptations of aquatic plants to terrestrial plants.
- The aerenchymal tissue in shoots and leaves, in which air collects, is important for gas exchange and buoyancy.
- In the case of floating leaves, the guard cells are located on the upper side of the leaf because no gas exchange can take place on the underside.
- The leaves of floating leaf plants are often particularly large in order to achieve better buoyancy and a higher rate of photosynthesis.
- If the little carbon dioxide that was able to get into the plants through the guard cells is not enough, they are dependent on dissolved carbon dioxide in the water.
- Some hydrophytes are leaf dimorphic. This means they form two different leaf shapes; usually one under the water and one over the water.
- Submerged hydrophytes can be pollinated by the water, others briefly stretch their flowers above the water surface.
- Aquatic plants that live in sea water also have to adapt to the effects of salt water, which also makes them halophytes.
- Few submerged aquatic plants have evolved into carnivorous plants due to the low nutrient supply in the water. An example of this is the waterfall.
hydrophyte examples
Two interesting and quite different examples are the waterfalls and the water lilies. Waterfall is an aquatic plant that has evolved into a carnivorous plant to meet its nutritional needs due to the lack of nutrients in the water bodies.
Water falls
Waterfall is a carnivorous plant of the sundew family. It is a submerged pleusophyte.
This means that it grows mostly under the water surface, but is not anchored to the water bottom with roots. With its trap, the trapping leaves, which fold up when potential prey approaches, it catches small animals such as water fleas or mosquito larvae. The captured prey is then broken down by digestive juices. This species can be found in clean, nutrient-poor, light-colored water, but is relatively rare.
water lily
The water lily is probably the best-known aquatic plant. It is very widespread in standing or slow-flowing freshwater in temperate, subtropical and tropical areas. The floating leaves of the white water lily can grow up to 30 cm and float individually on the water surface. The flowers also float individually on the water surface and can reach a size of up to 14 cm. The water lily is anchored to the bottom of the water with its roots.
Hydrophytes – The most important thing
- Hydrophytes (or aquatic plants) are plants that live wholly or partially in fresh, brackish or sea water.
- Hydrophytes can be divided into pleustophytes, rhizophytes and litoral helophytes according to various characteristics.
- In contrast to microphytes (microscopic algae), all hydrophytes that can be identified as individuals with the naked eye are also called macrophytes.
- Roots of hydrophytes mainly have the task of fixing the plant.
- The shoot axis is responsible for gas exchange.
- The structure of the leaves of hydrophytes differs depending on the aquatic plant species.
- Hydrophytes are adapted to their habitat in different ways.
proof
- Thomas. (2018) Fundamentals of plant ecology. jumper…