Wechselblatt waterweed

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Wechselblatt waterweed
Lagarasiphon major, Howardian, August 1992 (34388714862) .jpg

Change leaf waterweed ( Lagarosiphon major )

Systematics
Monocots
Order : Frog-spoon-like (Alismatales)
Family : Frog bite family (Hydrocharitaceae)
Subfamily : Anacharidoideae
Genre : Lagarosiphon
Type : Wechselblatt waterweed
Scientific name
Lagarosiphon major
( Ridl. ) Moss

The changeable leaf waterweed ( Lagarosiphon major ) is a species of the genus Lagarosiphon within the frog-bite family (Hydrocharitaceae). This water plant is native to southern Africa . It is used as a freshwater aquarium plant.

It is a neophyte in some areas of the world . Because of its invasive nature, it has been included in the European Union's list of Invasive Alien Species of Union Concern. Their sale is prohibited in all European countries.

Description and ecology

Vegetative characteristics

Lagarosiphon major is a perennial herbaceous plant . This aquatic plant grows immersed ( submerged ). It is anchored in the bottom of the water with a rhizome on which unbranched roots form to the side of nodes ( adventitious roots ). The stem has a diameter of 3 millimeters and a maximum length of about 5 meters; it is stiff and upright growing due to enclosed gas bubbles (lacunae).

The sessile, sessile leaves are alternate , sometimes whorled . They are loosely distributed in the lower shoot section and condense towards the tip of the shoot. The soft but stable, non-translucent leaf blade is linear with a length of 6.5 to 25 millimeters and a width of 2 to 4.4 millimeters with a mostly blunt, rarely pointed upper end and is protruding to slightly bent back. The leaf margin is transparent (hyaline) and very finely serrated through several rows of sclerchymatic fibers, with about 50 to 100 teeth on each side. The midrib of the leaf blade protrudes on the underside.

Generative characteristics

Lagarosiphon major is dioecious, separate sexes ( diocesan ), so male and female flowers sit on different individuals. Introduced populations only consist of plants of one sex, so they can only reproduce vegetatively (torn off parts of the shoot can take root and create new plant clones). The male inflorescences are surrounded by a bract ( spathe ), the two bracts are egg-shaped with a length of 3 to 5 millimeters. The inflorescence contains numerous (up to 50) relatively small flowers that bloom one after the other, the flower buds detach and rise to the surface of the water before they bloom. There the blooming flowers sail, driven by the wind, until, with luck, they meet a female flower, they have a "sail" made of sterile stamens (staminodes). The flower sleeve (Perianth) is pink, it consists of three approximately 1.25 millimeters long sepals and three approximately 1 millimeter long petals . The spathe of the lateral female inflorescences consists of two ovate bracts with a length of about 3.5 millimeters, on both sides with two to three teeth, each inflorescence contains only one to three flowers. Inside the flower cover , Lagarosiphon major forms gas bubbles, through which the long-stalked flowers are raised to the surface of the water in order to be pollinated by the floating pollen , this stalk can reach about 15 centimeters in length (if the water surface is not reached, it dies). The sepals are slightly wider than the petals of the rose-colored flower envelope, both are about 1.25 millimeters long. There are sterile staminodes available. There are three red scars on the ovary.

The capsule fruit is egg-shaped with a length of 4 to 5 millimeters and contains about nine seeds. The seeds are elliptical with a length of about 2 millimeters.

The number of chromosomes is 2n = 22.

Differentiation from similar species

The Wechselblatt waterweed is similar to other waterweed species of the genera Elodea and Egeria as well as the ground nettle ( Hydrilla verticillata ). Typically, the shoots are larger than Elodea , but smaller than Egeria . The leaves are alternate, sometimes almost whorled to three to four. The leaves of Elodea sit in threefold whorls, those of Egeria and Hydrilla in four- to five-fold. The leaves of the Wechselblatt waterweed are stiffer than those of the related genera, they keep their shape when the shoot is lifted out of the water. In addition, the leaves are similarly curved towards the tip of the shoots as the lower ones, in the related genera they are more upright.

Locations

Lagarosiphon major - blooming in the French lake Salagou.

Lagarosiphon major grows in, mostly relatively shallow, inland waters . In investigations in South Africa, they usually occur in waters with a water depth of less than 1.5 meters, near the shore, where they can build up very dense populations. They mostly occur in stagnant waters such as reservoirs, ponds and ponds, but also in the bank zone of flowing waters. They continue to grow through the winter. The average water temperature in the investigated waters was around 22 ° C (maximum in summer: 29.1 ° C). The waters are basic ( pH values over 8), relatively good conductive (250 to 330 µS ), mostly clear and rich in oxygen . In New Zealand, Lagarosiphon major was found to a depth of 6.5 meters, both on muddy and sandy bottom, as well as in nutrient-poor waters. In Europe, too, it thrives best in shallow, mostly relatively nutrient-rich, alkaline waters with a sandy bottom , but disappears in highly eutrophic waters. It is sensitive to wind exposure and waves and therefore prefers protected locations. Lagarosiphon major dies in frost, but can regenerate from deeper water that is not completely frozen.

distribution

The natural distribution area of Lagarosiphon major is in Southern Africa: It includes the west of the Republic of South Africa , south and east to the Cape Province , in the Orange Free State and Transvaal and the west of Zimbabwe . Lagarosiphon major was at times a popular aquarium and garden pond plant that was offered through various trade routes and was thus carried off almost worldwide. Naturalized, neophytic occurrences have been known for a long time, especially from Europe and New Zealand.

Occurrence in New Zealand and Australia

Lagarosiphon major was first registered outdoors in New Zealand in the 1950s. As early as 1957, it was considered harmful in Lake Rotorua . Since then, it has spread almost across the country, with increasing occurrences being noted in the South Island since around 1980. In some cases, it completely displaced the previously introduced Canadian waterweed from the waters. The species was initially introduced, often intentionally, as an ornamental plant or for water improvement by sport fishermen. In 1982, the trade in Lagarosiphon major was banned in New Zealand . Initially, however, this actually led to a deterioration, as many plants were illegally disposed of in natural waters. Although three small introduced occurrences have become known in Australia, the species has not been able to establish itself here permanently.

Occurrence in Europe

Lagarosiphon major is widespread in Europe, but is only considered a truly invasive species in Ireland , threatening local biodiversity . There are also deposits in England (first recorded in 1944 in a limestone quarry near Arlesey, Bedfordshire ), Austria, Switzerland, Germany, Belgium, France and Italy.

Occurrence in Germany

The change-leaved waterweed was first recorded in Germany in 1966. Status in Germany: The species is established in Germany. Frequent occurrences are in densely populated areas, including in inland waters in the catchment areas of the Isar in Bavaria and the Rhine in North Rhine-Westphalia and Rhineland-Palatinate . Individual occurrences also in inland waters of the catchment areas of the Vechte in North Rhine-Westphalia; Elbe in Saxony-Anhalt; Werra in Hesse ; Or (Juesse) in Lower Saxony .

Propagation paths

The alternate-leaved waterweed spreads exclusively vegetatively outside of its home in southern Africa. Torn off shoot fragments containing buds are drifted in the water. They can remain viable for months and when they come into contact with the ground they can take new adventurous roots.

Intentional Paths:

Introduction: aquaristics , ponds and botanical gardens

Unintentional Paths:

Application: Aquaristic (improper disposal of aquarium and pond plants).

Spread: Spread through fishing and fishing accessories, in or on devices / machines / equipment, by bio-vectors (e.g. duck birds ); Drift along rivers and canals with reaching new river catchment areas. Probable spread along rivers and canals. Spread to other still or non-contiguous rivers is unlikely and only possible with the help of (bio) vectors.

Combat

A mowing boat collecting cut macrophytes.

Lagarosiphon major is fought as an undesirable, invasive neophyte in many regions. By placing it on the list of invasive alien species of Union concern , the European authorities are obliged to record the distribution of the species and draw up management plans for their area. Control using herbicides is possible, but is prohibited in most countries due to their environmental impact. Mechanical control by mowing or tearing out is often attempted , with varying degrees of success . Mowing can even promote the spread of the plant through individually drifting pieces of shoot. In Ireland good results have been reported for covering with jute fabrics.

The possibilities of a biological control of the species are scientifically investigated. Before releasing potentially effective enemies, however, their way of life and potential for spreading must be examined extremely carefully, since in some cases species introduced for this purpose have ultimately caused worse ecological and economic problems than the species they were intended to control. In a study in the natural habitat in South Africa, a number of herbivorous insects were found on Lagarosiphon (a weevil of the genus Bagous , two butterfly caterpillars from species of Acentropinae (Nymphulinae), two mining fly species), the most promising of which was later identified as a new species Hydrellia lagarosiphon (family of Salt flies or Ephydridae) has been identified.

Systematics

It was first described in 1886 by the British botanist Henry Nicholas Ridley as the variety Lagarosiphon muscoides var. Major Ridl. of the species Lagarosiphon muscoides Harvey . She received the species rank Lagarosiphon major (Ridl.) Moss by Charles Edward Moss (in an article by the South African biologist Vincent A. Wagner ). A synonym for Lagarosiphon major (Ridl.) Moss is Lagarosiphon crispus Rendle . Derived from this, this plant species was common in the gardening trade for a long time under the gardener's name " Elodea crispa " or " Anacharis crispa ".

The genus Lagarosiphon comprises nine species, all of which are distributed in southern Africa (including the island of Madagascar). Lagarosiphon forms with a number of related genera (including Egeria ) the subfamily Anacharidoideae within the frog-bite family (Hydrocharitaceae), this position was also supported by molecular genetic analyzes ( phylogenomics ).

Individual evidence

  1. ^ AA Obermeyer: The South African Species of Lagarosiphon. In: Bothalia. Volume 8, 1964, pp. 139-146.
  2. ↑ a b c JJ Symoens, L. Triest: Monograph of the African Genus Lagarosiphon Harvey (Hydrocharitaceae). In: Bulletin du Jardin botanique National de Belgique. Volume 53, Issue 3/4, 1983, pp. 441-488. JSTOR 3667803
  3. ^ A b J. Matthews, R. Beringen, FPL Collas, KR Koopman, B. Odé, R. Pot, LB Sparrius, JLCH van Valkenburg, LNH Verbrugge, RSEW Leuven: Knowledge document for risk analysis of the Non-native Curly Waterweed (Lagarosiphon major) in the Netherlands . Ed .: Radboud University Nijmegen, Institute for Water and Wetland ResearchDepartment of Environmental Science, FLORON & Roelf Pot Research and Consultancy. Nijmegen 2012, p. 43 ( ru.nl [PDF]).
  4. ↑ a b J.-R. Baars, JA Coetzee, G. Martin, MP Hill, JM Caffrey: Natural enemies from South Africa for biological control of Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae) in Europe. In: Hydrobiologia Volume 656, 2011, pp. 149-158. doi: 10.1007 / s10750-010-0427-0
  5. ^ A b Clinton D. McCullough: A review of the aquatic macrophyte family Hydrocharitaceae (Angiospermae) in New Zealand. In: Tane. Volume 36, 1997, pp. 181-195.
  6. ↑ Shakira Stephanie Elaine Azan: Invasive aquatic plants and the aquarium and ornamental pond industries. Ryerson University Theses and dissertations Paper 818. 2011. download
  7. ↑ a b Tobias O. Bickel: Lagarosiphon major (Ridley) Moss ex Wagner (curly water weed). In: Robert A. Francis (Ed.): A Handbook of Global Freshwater Invasive Species. Earthscan, London 2012, ISBN 978-1-84971-228-6 , Chapter 7.
  8. ↑ a b Wechselblatt waterweed. Management and action sheet for Regulation (EU) No. 1143/2014. (PDF) In: Environment.hessen.de. February 2018, accessed July 9, 2019 .
  9. ↑ major (Ridl.) Moss, Große Scheinwasserpest & Wechselblatt-Wasserpest. In: FloraWeb.de.
  10. ↑ A. Hussner, I. Stier, MJJM Verhofstad, ES Bakker, BMC Grutters, J. Haury, JLCH van Valkenburg, G. Brundu, J. Newman, JS Clayton, LWJ Anderson, D. Hofstra: Management and control methods of invasive alien freshwater aquatic plants: A review. In: Aquatic Botany. Volume 136, 2017, pp. 112-137. doi: 10.1016 / j.aquabot.2016.08.002
  11. ↑ Joseph M. Caffrey, Michael Millane, Stephanie Evers, Helen Moran, Martin Butler: A novel approach to aquatic weed control and habitat restoration using biodegradable jute matting. In: Aquatic Invasions. Volume 5, Issue 2, 2010, pp. 123-129. (open access) doi: 10.3391 / ai.2010.5.2.01
  12. ^ A b Donald H. Les, Nicholas P. Tippery: In time and with water. . . the systematics of alismatid monocotyledons. In: P. Wilkin, SJ Mayo (Ed.): Early Events in Monocot Evolution. Cambridge University Press, 2013, ISBN 978-1-139-00295-0 , Chapter 6.

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