Water nut

Water nut
	Water hazel ( Trapa natans )
Systematics
	Rosids
	Eurosiden II
Order :	Myrtle-like (Myrtales)
Family :	Loosestrife family (Lythraceae)
Genre :	Trapa
Type :	Water nut
Scientific name
	Trapa natans
	L.

The water nut ( Trapa natans ), like the not closely related species Eleocharis dulcis also called water chestnut , is a plant species within the loosestrife family (Lythraceae). It occurs in temperate and subtropical zones in Europe, Africa and Asia. The annual aquatic plant is threatened with extinction in Germany and has been a nature reserve since 1987.

description

illustration

Flower and leaves

fruit

The water nut is a deciduous, annual herbaceous plant . It occurs in stagnant waters, but also in the Danube from Belgrade , and is anchored in the ground at a depth of 30 to 60 centimeters. Their petioles float so that the fan-shaped leaves float like a rosette on the surface of the water. However, the leaves do not appear until June, they turn red in autumn and then die.

The flowering period extends from July to August. Its inconspicuous flowers are white and have radial symmetry . A dark brown, hard-skinned fruit develops, which is reinforced at two, often four ends with pointed thorns , with which it can anchor itself in the lake bed. It contains a white core made up of 20% starch ; at least cooked, it is edible.

The number of chromosomes is 2n = 40, 48 or approx. 36.

ecology

The water nut is a summer annual plant. This hydrophyte or floating leaf plant has roots 1 to 3 meters long, anchored by the fruit in the mud. The stomata of the leaves are on top. There are also lobed, submerged leaves without stomata. Acid- secreting glands can be found on the underside of the leaf as well as on the stem , which are interpreted as protection against eating by aquatic animals. There are paired secondary roots with four rows of green, photosynthetically active side roots each.

From an ecological point of view, these are nectar-bearing "small funnel flowers". Self-pollination prevails.

The fruits are solitary, stone-fruit-like nuts enclosed by the enlarged flower axis when ripe . The valve-shaped sepals were transformed into four (rarely two) thorn-like, barbed projections, which later serve to anchor them in the ground. Swimming, Velcro spreading by water birds and human spreading takes place, whereby the plant became a cultural refugee and a cultural relic. Fruit ripens from September to October. The seeds are heat germinators and have no nutrient tissue themselves . One of the two cotyledons serves as a starch store and remains in the fruit, the other is flake-shaped and emerges from the fruit with the sprout stem. In its armpit, next to a side shoot, two buds later detached and used for vegetative reproduction arise.

Occurrence

The water nut can be found in the Mediterranean region , in Central and Eastern Europe as well as in Central and South Asia, on Taiwan , Japan and in Central Africa .

The preferred habitat are low-lime, but nutrient-rich backwaters that are warm in summer, humus mud lakes and ponds. It can be found almost only in the lowlands in heat-favored regions. In Central Europe it is a type of trapetum from the Nymphaeion association.

In Germany , too , the water nut used to be widespread, as is indicated by finds at the Federsee . Around 1690, Matthäus Prätorius reported that there were still large deposits in East Prussia. In 1962, Horst Koehler described the Linkehner See near Tapiau in East Prussia as one of the last "German" occurrences in The Practical Garden Book . In Baden-Württemberg there are still two stocks in the nature reserves Altrhein Kleiner Bodensee and Rußheimer Altrhein-Elisabethenwört , in Bavaria in Scheyern Monastery , in Brandenburg in Drobschsee and on the Old Spree , which leads into the Schwielochsee , and in Saxony-Anhalt in the Schönitzer Lake . In Germany, the water nut is on the Red List of Endangered Species as critically endangered.

Endangered plant species on Latvian postage stamp

In Austria the water nut occurs only in the far east. While it is extremely rare in Lower Austria , it is one of the invasive species south of the main Alpine ridge, in Burgenland and in Eastern Styria, and has become a problem plant in many fish ponds (ponds near Güssing ).

use

Archaeological investigations find large quantities of water nuts, especially in Eastern Europe, which prove their extensive use in food at least since the Neolithic . In the vicinity of the Upper Swabian pile dwellings, for example on the Federsee , they evidently formed an important food source in the Neolithic period.

The fruit of the water nut is edible but must be heated to reduce toxicity . In Japan the plant is called " hishi " ( 菱 , ひし ), in China " ling " ( 菱 , líng ), and has also been used in folk medicine, but its medicinal effect has not yet been clearly scientifically proven.

Others

In Southeast Asia, the giant intestinal leech ( Fasciolopsis buski ) of humans and pigs is transmitted to the surface of the water nut by means of its cercariae . Various other parasites can also be transmitted through raw consumption of aquatic and marsh plants .

In 2011, the water nut was named Aquatic Plant of the Year in Austria, Germany and Switzerland .

Systematics

Trapa natans var. Bispinosa

Two varieties of the species Trapa natans L. have been described:

Trapa natans var. Bispinosa (Roxb.) Makino (Syn .: Trapa bispinosa Roxb. )
Trapa natans var. Natans

literature

Jakob Jäggi: The water nut, Trapa natans L. and the tribulus of the ancients. Naturforschende Gesellschaft in Zürich, Zürich 1883 ( Naturforschende Gesellschaft in Zürich. Neujahrsblatt 86, ISSN 0379-1327 ).
Water nut. In: FloraWeb.de.

Individual evidence

↑ ^a ^b ^c water nut. In: FloraWeb.de.
^ Jürgen Skop: TID Danube paddling tour . epubli, 2011, p. 30 (64 pp., Google.de [PDF] e-book).
↑ ^a ^b Erich Oberdorfer : Plant-sociological excursion flora for Germany and neighboring areas . With the collaboration of Angelika Schwabe and Theo Müller. 8th, heavily revised and expanded edition. Eugen Ulmer, Stuttgart (Hohenheim) 2001, ISBN 3-8001-3131-5 , pp. 681 .
↑ ^a ^b ^c 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 .
↑ Living Rhine meadows - water nut (PDF; 49 kB)
↑ On the Spree meadows south of Beeskow (PDF; 213 kB) Nabu, accessed on September 22, 2011
↑ Y. Hijikata, A. Yasuhara, Y. Sahashi: Effect of an herbal formula containing Ganoderma lucidum on reduction of herpes zoster pain: a pilot clinical trial . In: Am J Chin Med. , 2005, 33 (4), pp. 517-523, PMID 16173526 .
^ Dönges: Parasitologie , 1988
^ Trapa natans L. Taxonomic Serial No .: 27170. In: ITIS Report. Integrated Taxonomic Information System (ITIS), accessed November 12, 2017 .