Canadian waterweed ( Elodea canadensis )
The Canadian waterweed ( Elodea canadensis ) is an aquatic plant from the genus of the waterweed ( Elodea ) in the family of the frog-bite family (Hydrocharitaceae).
Occurrence and distribution
The plant, which originally comes from the temperate latitudes of North America and is mainly native to Canada, is one of the neophytes in Europe because it is alien here. Their settlement and spread in Europe was initiated by shipping and further promoted by targeted releases (e.g. of aquarium keepers) or by water birds.
Since the Canadian waterweed finds similar climatic conditions in Europe as in its homeland, it has spread rapidly, especially since it has no natural, population-regulating enemies here. They are now part of the common inventory of species in many still and flowing waters. The first evidence of its occurrence in Europe is in Ireland in 1836 . In 1859 she was settled in Berlin or abandoned. From there it spread across Central Europe in just 20 years. Only in the rare oligotrophic (nutrient-poor) lakes is it usually absent.
Elodea canadensis is dioecious ; in Central Europe, however, there are only specimens with female flowers (flowering period: May to August), so that no generative reproduction takes place. It spreads mainly via broken parts of the shoots that are drifted or, for example, attach to water birds.
The Canadian waterweed rises in the Allgäu Alps in the Tyrolean part in the Vilsalpsee near Tannheim up to 1160 meters above sea level.
The Canadian waterweed is an herbaceous plant . The submerged rungs reach a length of 30 to 100 centimeters. They can often form runners up to three meters long.
On the flooding stems , the small, dark green leaves are densely lively, usually in threes (two to four). They are one to three centimeters long, soft or rigid, tongue-shaped and rounded at the front, usually broadest in the middle, narrowed at the base, green to dark green in color and often coarse. The tips of the leaves are sometimes slightly bent back. The length of the leaves is two to five times their width (1.5 to 3.5 millimeters).
Their decussive (cross- opposite ) leaves (see Fig.) Are overall elongated and ovate to lanceolate in shape.
Compared to the narrow-leaved waterweed ( Elodea nuttallii ), the species appears more compact and more evenly leafed.
These are dioecious separate-sex ( diocesan ) plants. The inconspicuous, three to 5.5 millimeters small, whitish-light purple flowers sit on long whitish stems that protrude above the water surface or rest on it. The flower has greenish to reddish colored sepals and whitish petals , which are about the size of the sepals.
The species has chromosome numbers 2n = 24, 32, 40, 48, 56, 64, 72, 96.
The Canadian waterweed is a perennial, often evergreen aquatic plant that rarely survives with winter buds . In adaptation to the often low availability of carbon dioxide in stagnant water, the plant also uses the C4 path in addition to the C3 path during photosynthesis . The latter, however, does not follow the normal mechanism in that the sub-processes (storage of carbon dioxide and its processing in the Calvin cycle ) are not distributed among different cell types, but rather among different compartments of the same cell.
There are both purely male and purely female plants, although in Germany and large parts of Europe there are almost only female representatives. Therefore, it reproduces there almost exclusively in a vegetative way. It is believed that only female plants came to Europe at the time of naturalization around 1836. The plant was included in the black list of invasive neophytes in Switzerland because of its potential for spreading and the damage it causes in the areas of biodiversity , health and economy .
The Canadian waterweed blooms in the water between June and September. If both sexes are present in one lake, a turion formation occurs . Otherwise, the plant forms numerous vegetative offshoots that sprout again in spring.
Pollination of the flowers (water bloom - hydrophilicity ) and spread of seeds (water spread - hydrochory ) take place exclusively through the water.
The Canadian waterweed forms vegetation units together with other plants. It is a character species in the vegetation class Potamogetonetea pectinati ( spawn and floating leaf communities) and in the subordinate vegetation association Potamogetonion pectinati . It is particularly common to form Elodea canadensis societies as dominant populations with few species.
The Canadian waterweed has 18% protein , 43% starch and 2.5% fat when dry , making it a valuable fodder and fertilizer . After all, it serves as a popular ornamental plant in aquariums and garden ponds.
In school trials it is used to demonstrate photosynthesis , i.e. the production of oxygen during exposure.
- Ruprecht Düll , Herfried Kutzelnigg : Pocket dictionary of plants in Germany and neighboring countries. The most common Central European species in portrait. 7th, corrected and enlarged edition. Quelle & Meyer, Wiebelsheim 2011, ISBN 978-3-494-01424-1 .
- Christel Kasselmann : aquarium plants. Ulmer Verlag, Stuttgart 1995; 2nd, revised and expanded edition 1999, ISBN 3-8001-7454-5 , p. 286.
- ↑ Erhard Dörr, Wolfgang Lippert : Flora of the Allgäu and its surroundings. Volume 1, IHW, Eching 2001, ISBN 3-930167-50-6 , p. 141.
- ^ Tropicos. 
- ^ Federal Office for the Environment FOEN: Invasive Alien Species . ( admin.ch [accessed on August 6, 2019]).
- ↑ S. Buholzer, M. Nobis, N. Schoenenberger, S. Rometsch: List of the alien invasive plants of Switzerland . Ed .: Infoflora. ( infoflora.ch [accessed on August 6, 2019]).
- Canadian waterweed. In: FloraWeb.de.
- Canadian waterweed . In: BiolFlor, the database of biological-ecological characteristics of the flora of Germany.
- Profile and distribution map for Bavaria . In: Botanical Information Hub of Bavaria .
- Elodea canadensis Michx., Map for distribution in Switzerland In: Info Flora , the national data and information center for Swiss flora .
- Distribution in the Netherlands  (Dutch)
- Distribution in the northern hemisphere according to Eric Hultén 
- Thomas Meyer: Data sheet with identification key and photos at Flora-de: Flora von Deutschland (old name of the website: Flowers in Swabia )
- Neoflora (BfN): Invasive, alien plants in Germany: E. canadensis