Aquatic plant
Aquatic plants or hydrophytes (from ancient Greek ὕδωρ hýdōr , German 'water' and φυτόν phytón 'plant') are plants that live completely or partially under water. Aquatic plants are found in fresh , brackish and marine water .
Definition and demarcation
Macrophytes
The plants growing in water (in the broader sense, as species that use pigments such as chlorophylls from sunlight and inorganic nutrients as so-called photoautotrophs to generate their biomass) include the groups primarily living in water, known as algae , and some groups of primarily land-living, Mosses and vascular plants , ferns and flowering plants (representatives of the other seed plants have no aquatic representatives). " Blue-green algae " used to be counted among the algae , which today, like all autotrophic prokaryotes , are no longer considered plants. For methodological reasons, the study of aquatic plants has resulted in a dichotomy: the small (often single-celled) species of phytoplankton and algae growing as microscopic threads or beds (called periphyton ) are known from algae science (phycology, or algology) or Processed by limnologists (hydrobotanists) interested in production biology , they usually have to be determined in the laboratory using microscopic techniques. Usually they are not meant when we talk about aquatic plants. The larger aquatic plants, which can usually be approached in the terrain, are called aquatic (that is: in the water) "macrophytes". Vegetation experts usually only work on the macrophytes. The term macrophytes is purely pragmatically defined as those, larger, aquatic plants that can be identified and processed in the field using the usual vegetation methods. This includes all mosses and vascular plants and from the group of algae the chandelier algae . Certain other macroscopic algae, such as the red algae of the genera Lemanea and Batrachospermum (such as the frog spawn alga ), are sometimes included, sometimes not.
The only seed plants living in the sea are the grass-like species of the shore zone , which are grouped together to form seagrasses . Large types of seaweed , which are summarized as seaweed , are usually not included in the term aquatic plant.
Aquatic plants and marsh plants
The macrophytes of fresh water form, according to most systematics, a growth type or life form type of plants. The delimitation of aquatic plants from other plants is not clear and is handled somewhat differently by different botanists. While some include all species that grow in the water, at least temporarily, others only consider those species that have special adaptations to aquatic life, in particular that can assimilate in water (i.e. not only survive temporary flooding). Others even demand that the species must be able to complete its entire life cycle in the water. The problem with the delimitation is, for example, that some plant species exist in a water and in a land form, which can merge, so that the original water plant continues to grow on land after it has dried out. Other species take root under water, but partially protrude above the water surface, whereby they may or may not assimilate in the submerged parts. A distinction is made
- Hydrophytes (also Euhydrophytes or Limnophytes), aquatic plants in the narrower sense: Plants that can spend their entire life in water. Often they are able to take up dissolved hydrogen carbonate instead of carbon dioxide as a carbon source, some have the ability to pollinate underwater. If land forms occur at all, they are connected to the water via creeping rungs ( rhizomes or stolons ).
- Amphiphytes (also pseudohydrophytes): These are plants that can live in water as well as on land. For example, the European Strandling ( Littorella uniflora ) grows submerged on the bottom of the water, but also in the wet mud of dried out water or from its banks.
- Helophytes (also telmatophytes), marsh plants : These are plants that can stand in the water with the stem base or only the roots, but always protrude above the water surface and assimilate predominantly in the air space. They can usually just as well be found in ground-wet terrestrial (i.e., land-based) habitats. These include the types of reed beds , such as the reed ( Phragmites australis ). There are some doubtful cases, including flood-tolerant small grasses and herbs that normally live on land but can assimilate for a while submerged, such as water pepper ( Persicaria hydropiper ), or reed species that also assimilate with the submerged section of shoot, such as common pond rush ( Schoenoplectus lacustris) ). As a rule, however, the helophytes are not counted among the aquatic plants.
Types of aquatic plants
The classification of the aquatic plants (without the marsh plants) is carried out according to different criteria, depending on the subject or the question, so that different classification schemes are used side by side.
Growth forms
The subdivision of the aquatic plants according to the site-specific growth habit is the most frequently used classification scheme. One distinguishes
- Pleustophytes or floating plants. These are free-swimming macrophytes that do not take root in the water bed. Sometimes it is still finely differentiated into
- Rhizophytes (rarely: benthophytes). These are all actual aquatic plants rooted in the water bed.
- submerged (or submerged ) rhizophytes. These are the actual or typical macrophytes. These include the (native) thousand-leaf species (genus Myriophyllum ). They are sometimes referred to as diving leaf plants (rarely also diving plants). Often in nutrient-rich (eutrophic) lakes there is a separate diving leaf zone .
- Floating leaf plants. In floating leaf plants, the plant is rooted on the bottom of the water, the leaves float on the surface of the water. The assimilation takes place in the air space, over the leaf upper side which is not covered with water. This includes, for example, the white water lily ( Nymphaea alba ). Often in nutrient-rich (eutrophic) lakes there is a separate floating leaf zone.
Many aquatic plant species can belong to several types of growth habit. Species such as pure white water crowfoot ( Ranunculus ololeucos ) or yellow pond rose ( Nuphar lutea ), for example, have underwater leaves and floating leaves, often on the same plant.
Some botanists distinguish as a further group:
- Haptophytes. These would be plants anchored to the substrate without real roots. The term is rarely used, especially for water mosses such as the spring moss ( Fontinalis antipyretica ), which, like all mosses, has no roots and is anchored to the hard substrate of the water bed by means of rhizoids . However, the term has remained uncommon.
Shape types
In addition to the classification according to life forms, a second classification scheme is in use, which divides the aquatic plants into groups according to morphological similarity. It was first introduced by the Swedish botanist Gustaf Einar Du Rietz and later expanded. Confusingly, these are often also referred to as the "growth habit", so that this term is not unambiguous. In addition, schemes are also in use that combine both classification options. The growth forms, in this sense, are each named after a characteristic representative. The following terms are used, for example
- Nymphaeiden (after Nymphaea , water lilies ): plants with large or medium-sized floating leaves; submerged leaves absent or poorly developed.
- Vallisnerids (after Vallisneria ): Submersed plants with long linear submersed leaves, often without a shoot. Depending on the site conditions, sometimes also appearing as helophytes (e.g. swan flower Butomus umbellatus ).
- Elodeids (after Elodea ): Submerse shoot plants with whorled leaves that can completely fill the water body.
- Peplidae (after the marsh whale Lythrum portula , formerly Peplis portula ): Submersed shoot plants that can develop floating leaf-like rosettes of leaves.
- Myriophyllids (after Myriophyllum ): Submerged shoot plants with short, whorled, finely divided leaves.
- Parvopotamids (small spawning herbs, after the narrow-leaved species in the genus Potamogeton ): Submersed shoot plants with narrow, linear leaves.
- Magnopotamids (large spawning herbs, after the broad-leaved species in the genus Potamogeton ): Submersed shoot plants with broad leaves, rarely also floating leaves.
- Magnobatrachids (after the larger species of the genus Ranunculus , sub-genus Batrachium : water crowfoot ): Submersed shoot plants with long, finely divided leaves. Plants longer than 2 meters, occasionally with small floating leaves.
- Parvobatrachids (after the small-grown water cockfoot species): Submerse shoot plants with short, finely divided leaves, occasionally with floating leaves. Plants shorter than 2 meters, often forming landforms.
- Isoetiden (after Isoetes ): Submerged plants with a short shoot and short rigid leaf rosettes.
- Chariden (after the chandelier algae of the genus Chara ): Submerse macroalgae with a whorled branched shoot system.
- Stratiotids (after the crab claw Stratiotes ): Plants swimming in the water, whose vegetative parts can partly protrude above the water surface and whose roots are optionally anchored in the sediment.
- Beruloiden (after Berle Berula erecta ): completely submerged growth form of dicotyledonous marsh plants.
- Lemniden (after Lemna ): Small plants floating on the surface of the water.
- Ricciellids (after the Riccia star liver moss ): Small plants that swim under the surface of the water.
- Ceratophyllids (after Ceratophyllum ): Large plants floating in the water body with finely divided leaves, occasionally with rhizoids.
- Hydrocharides (after the frog bite Hydrocharis morsus-ranae ): Larger plants with floating leaves on the water surface float.
Adjustments
Aquatic plants are adapted to their habitat in different ways, depending on their growth form and location. All aquatic plants are herbaceous plants.
- Many aquatic plants that do not grow exclusively submerged (submersed) have air conduction tissue ( aerenchyma ) through which oxygen can get into the stems and roots.
- Floating leaves usually show a particular structure: they have a distinct Aerenchym and are thus buoyant, the stomata are limited to the air-exposed top; The surface of the leaf is water-repellent due to a layer of wax, partly also dirt-repellent ( lotus effect ); they have gland-like structures with which they can absorb water and ions ( hydropots ); the leaf stalks are very elongated, but otherwise normal, they also have xylem , with which they transport the water from the roots to the transpiring leaves. However, the water is transported through root pressure , not through perspiration suction. In still waters, the floating leaves are usually large and round and arise from a rosette. Victoria (genus) forms leaves up to two meters in diameter.
- Free swimming plants are sometimes greatly reduced, such as swimming ferns or algae ferns . The most reduced flowering plants are the duckweed family: Wolffia no longer forms any roots or vascular bundles, the leaves are reduced to button-like thalli .
- For photosynthesis, submersed plants are dependent on the much lower content in the water for their carbon dioxide supply . Submersed plants in still waters therefore have narrow or slashed leaves ( waterweed ). The cuticle is thin. The chloroplasts are located in the epidermis , which in plants is normally free of chloroplasts. This reduces the diffusion path of the carbon dioxide. Due to the lack of transpiration , they cannot absorb any mineral salts from the soil. Your xylem is reduced. The roots are only used for anchoring. But since the water also has a low nutrient content, the water hoses and the water trap have developed into carnivorous plants .
- Some of the submerged plants are also pollinated by the water ( hydrophilicity ). Others, however, stretch their flowers into the air and are pollinated by wind or animals.
- In addition to the factors already mentioned, plants in rapidly flowing waters are also exposed to mechanical stress. On the other hand, the supply of carbon dioxide and nutrients through the movement of the water is better than in standing water. They usually have cord-like stem axes with a centrally located, solid xylem. The leaves are usually finely divided. Examples are the species group water crowfoot . However, they can also form leaves outside the water that resemble normal leaves. A plant therefore forms two different leaf shapes ( heterophylly ). Another group in fast-flowing waters are the Podostemaceae in tropical rivers.
- Plants in sea water, such as sea grasses , mangroves and plants from the salt marshes, also have to cope with the physiological effects of the sea salt, compare salt plants .
- As hydromorphy refers to the special design of organs, the underwater occur (eg. As stems and leaves in water and semi-aquatic plants).
- Many aquatic plants are heteroblastic, leaf-dimorphic . In the course of its development, a plant forms two completely different leaf shapes.
See also
Individual evidence
- ↑ a b Gerhard Wiegleb (1991): The life and growth forms of macrophytic aquatic plants and their relationships to the ecology, distribution and socialization of species. Tuexenia 11: 135-147.
- ↑ Heinz Ellenberg : Vegetation of Central Europe with the Alps in an ecological, dynamic and historical perspective. 5th, heavily changed and improved edition. Ulmer, Stuttgart 1996, ISBN 3-8001-2696-6 , p. 436.
- ↑ a b Peter Englmaier (2014): The macroflora of fresh water. Denisia 33. pp. 313-345.
- ^ Alfred E. Schuyler (1984): Classification of Life Forms and Growth Forms of Aquatic Macrophytes. Bartonia 50: 8-11.
- ↑ G. Wiegleb, B. Zander, U. Wohlfahrt (1992): Typification and assessment of flowing water vegetation in the Federal Republic of Germany. Final report. On behalf of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety. Carl von Ossietzky University of Oldenburg, 344 pages.
- ↑ Helmut Mühlberg (2010): Growth forms of aquatic angiosperms (Part 1). Bad Endalia 20: 5–20.
- ↑ Roland Ennos, Elizabeth Sheffield: Plant Life. Blackwell Science, Oxford et al. 2000, ISBN 0-86542-737-2 , pp. 171-189.
- ^ Eduard Strasburger (founder): Textbook of botany for universities. 32nd edition, 1983. Gustav Fischer Verlag, Stuttgart 1983. ISBN 3 437 20295 2 . Section Aquatic Plants, page 190 ff.
