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2019

European Frogbit (Hydrocharis morsus- ranae) is the aquatic plant of the year 2019

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European frogbit (Hydrocharis morsus-ranae)



Hydrocharis morsus-ranae (Source: Ralph O.Schill)

By selecting the European frogbit as the aquatic plant for the year 2019, we want to raise awareness for the endangerment of shallow water habitats, which are an important habitat for aquatic animals and plants.

The heartshaped floating leaves of the European frogbit resemble those of water lilies. The leaves are round to kidney-shaped and are shining green on the top. The bottom is slightly reddish. Leave veins are on both sides of the stalk with two bow-shaped, unbranched main veins. The diameter of the floating leaves is 1.5 - 5 cm. At the beginning of the leave stalk are also two approx. 2 cm long, narrow stipules. Numerous roots are hanging into the water to take up nutrients out of the water column. Only in very shallow areas they are actually attached to the sediment. The plant leaves grows in rosettes and by growing stolons of 5 - 20 cm length, new rosettes (daughter plants) grow at the end of the stolons. Thus, the plants form dense vegetation patterns.

Schwimmblatt-Teppich aus Froschbiss

Dense frogbit vegetation (Source: Ralph O. Schill)

The species is monoecious, growing female and male flowers on the same plant. Female flowers (1-2 cm) are somewhat smaller and stand alone. Male flowers are up to 3 cm in diameter and can grow singly or in groups of up to three on 2 - 6 cm long stalks. The three white petals have a yellow base.








Wintering buds (Source: Volker Krautkrämer)

In colder water, like e.g. in Finnland, frogbit sometimes does not flower. This is not absolutely necessary for the propagation. During the vegetation persiod, stolons grow fast and in high numbers with small rosettes which can detach from the parent plant. Thus, the floating rosettes can slowly disperse. In most cases, however, the stolons grow into a dense, intertwined mass of frogbit.



During fall, wintering buds form which will be buried in the sediments protecting them from winter frosts. As soon as the watertemperature is increasing during spring and early summer, the winter buds start to grow leaves, in which oxygen is stored. When sufficient leaves have grown, the plant's buoyancy is lifting it to the water surface.






Occurence and Distribution



Frogbit leaves with bow-shaped veins (Source: Volker Krautkrämer)

Frogbit prefers slow moving or protected lentic, warm and nutrient-rich water bodies. It is native to Europe and parts of Asia. In Germany, it is mainly found in the lowlands of northn Germany.






Threats



Hydrocharis morsus-ranae (Source: Ralph O.Schill)

Within Germany frogbit is endangerd or highly endangered with the exception of Schleswig-Holstein.
In Austria frogbit occurs in all federal regions except Tirol and Vorarlberg, however, it is highly endangered.
Forgbit is absolutely protected in the cantons of Thurgau and Waadt in Switzerland.









Interesting facts

The botanical name Hydrocharis morsus-ranae was created from the Greek words for "water" as well as "grace and beauty". The Dutch botanists Lobelius and Dodonaeus mention frogbit for the first time in the second half of the 16th century. The name "frogbit" does not refer to frogs actually biting into the leaves. It is more a reference to the shallow water, near-shore habitat of the floating-leaves plant, which is similar to habitat prefered by frogs. The "bite" can also explained with the indented leaf base, which looks a little bit like being bitten. Even in other languages the name refers to the frogbite: Dutch (kikkerbeet), German (Froschbiss) or Norwegian (froskebitt).

Frogbit is a neophyte



Froschbiss Ausläufer (Source: Volker Krautkrämer)

Planted in garden ponds, frogbit got into the region of Ottawa (Canada) in 1938. Since then it is spreading as an invasive neophyte in different regions of Cananda. In 1993 it was disciverd in the US state of Vermont. At the moment, it is known to occur in Maine, Michigan, New York, Pennsylvania and Washington.





Text und Bilder von PD Dr. Ralph O. Schill und Volker Krautkrämer