Salvinia natans
Common water fern ( Salvinia natans )
The common water fern ( Salvinia natans ), also called Common water fern, is a water plant from the group of ferns belonging to the family of Schwimmfarngewächse ( Salviniaceae ).
Description
The species is an annual plant that floats horizontally on the water surface, the roots are under water and are free floating, not anchored in the ground. Stems of the plant are 5 to 10 centimeters long. The leaves are arranged in whorls threefold and are fundamentally different in structure and function ( Heterophyllie ):
The top two are floating leaves. They possess inside many air chambers ( intercellular spaces ) and ensure, by correspondingly low density, buoyancy. On the epidermis sit numerous, crown-shaped trichomes. They are non-wettable by coating with wax with water. After submerging an air jacket is held as between the stiff hairs that give the plant an extra boost to quickly re-emerge to the surface.
The third leaf, the water sheet is submerged as the scion. It is finely divided and appear stringy and hairy. This gives it a very large surface area over which it absorbs dissolved nutrients from the water. It resembles not only externally a root, but also fulfills the function of the substance from the environment. In contrast to the floating leaves the water journal contains no chlorophyll and is therefore not capable of photosynthesis.
While the floating leaves are oblong- elliptical in shape with natans Salvinia, they are for example in the species group Salvinia auriculata agg. rather roundish - oval.
Ecology
The common water fern is predominantly annual and ungleichblättrig, ie the leaves are arranged in whorls of three -fold. The top two are designed as floating leaves. The bottom, facing the water, is finely divided as the " Water Leaf " and divided into root-like sections. Real roots are missing. The floating leaves are internally equipped with large air chambers and fitted on the top with upright, slightly curved, long hair and therefore water repellent ie Water droplets remain as "pearls" are on the hair - air cushion. In this way, the stomata are protected from the gas exchange debilitating wetting with water. When submerging the hair pull with air bubbles, draw the leaf immediately to the water surface.
Propagation
The propagation conditions are quite complicated. There is Verschiedensporigkeit or heterospory. Micro-and megaspores groups are each enclosed in a sterile sheath, the indusium, which fruit -like structures, called Sporokarpien arise. In megasporangium, a single megaspore, which is surrounded by a sporangium and later with this detached from the mother plant and overwinters in mud soil developed. In the megaspore the multicellular female prothallus grows up in this then after fertilization the embryo. In the spring sprout from the megaspores new plants, which can then ascend to the surface. Sporenreife is from August to October.
Distribution and habitats
The species is widespread in summer warm areas of Eurasia, with a focus on East Asia and in South and Eastern Europe. In central Europe it occurs rarely, about an der Oder, the Havel and the Middle Elbe and in the Upper Rhine from Karlsruhe to Offenbach am Main in Bavaria. In the Red List of Germany Salvinia natans is classified as endangered. In Austria and Switzerland, the Art in North America was missing she introduced as an aquarium plant.
The common water fern is a heat- loving and nutrient- vulnerable type, which occurs preferentially in sheltered backwaters and lake bays. There is a water fern Kennart the Society, but occasionally it is also found in other water lens companies.