Salvinia molesta

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Salvinia molesta
Salvinia molesta.jpg

Salvinia molesta

Systematics
Ferns
Class : True ferns (Polypodiopsida)
Order : Floating ferns (Salviniales)
Family : Swimming fern family (Salviniaceae)
Genre : Swimming ferns ( Salvinia )
Type : Salvinia molesta
Scientific name
Salvinia molesta
DS Mitchell

Salvinia molesta is a type of swimming fern ( Salvinia ) originally from Brazil. The species has been abducted worldwide and can have a negative impact on the usability and biodiversity of water bodies worldwide. Salvinia molesta is included in theEuropean Union's list of invasive alien species of Union- wide importance and in theIUCN 's list of " 100 of the World's Worst Invasive Alien Species ".

features

Salvinia molesta , hairs on the water-repellent upper side of the leaf with the "whisk-shaped" hairs

Like all swimming fern species, Salvinia molesta is a non-rooting species of aquatic plant (a " pleustophyte ") that drifts freely on the surface of the water and can often form dense mats. The short rungs carry leaf whorls made up of three leaves each, two floating leaves and one strongly slashed, root-like underwater leaf. The floating leaves, which often overlap each other widely, are round to elliptical when young and often folded in a little along the midrib, wider than long with age, they reach about 12 to 30 millimeters in length by 15 to 50 millimeters in width. They have entire margins and often have a bit of a margin at the tip. The leaf shape and size is very varied depending on the ecological conditions, some botanists differentiate between three growth forms. As is typical for swimming ferns, they are densely covered with papillae on the surface, hairy protruding and not wettable. The shape of these hairs is typical of the South American Salvinia auriculata species group to which the species belongs. Four hairs (rarely two) stand close together and initially spread apart, but are bent back towards the tip and united in a common tip, this shape has been compared to a whisk for whipping cream. This feature clearly distinguishes it from the common swimming fern Salvinia natans, native to Europe, and from Salvinia minima , which is neophytically widespread in North America . The underwater leaf is 25 to 300 millimeters long, heavily branched and densely covered with brown hair.

The differentiation of the species of the Salvinia auriculata species group from one another is not easy. The main axis of the submerged leaves is important, which in Salvinia molesta is straight, not curved towards the tip. Fertile (spore-forming) leaf sections of the submerged leaves carry spherical to egg-shaped spore containers ( called sporocarp ), which sit in two rows, relatively loosely, on a branched axis with very short, non-curved distal branches. Salvinia molesta , however, reproduces exclusively vegetatively, in the remarkably small sporocarps never mature spores are formed.

Phylogeny, taxonomy, systematics

Salvinia molesta forms the Salvinia auriculata species complex with the species Salvinia auriculata Aubl., Salvinia herzogii de la Sota and Salvinia biloba Raddi . The species in this group occur, often side by side, in tropical South America. Salvinia molesta was originally unknown from there and was described by Mitchell in 1972 after plants from Africa ( Kariba dam in Zimbabwe ).

The species is polyploid with five sets of chromosomes from two different species (allopentaploid) and reproduces exclusively vegetatively, since no mature spores can be formed; it is therefore considered certain that it is due to a hybridization of two species (probably Salvinia biloba and Salvinia herzogii ), which possibly only took place in culture.

Some botanists consider Salvinia adnata Desv. for the valid name of this species, which was first described in 1827 using a sterile, neophytic specimen (from the island of Réunion ). Whether it is the same species as Salvinia molesta , however, is controversial, since one of the suspected parent species, Salvinia biloba, also often trains sterile individuals, the differentiation is difficult. It was therefore suggested that this name should be suppressed in the interests of nomenclature stability.

Genetic studies indicate that the New World species of the genus Salvinia form a clade . The association of the Salvinia auriculata species group could also be confirmed in this way.

distribution

The species, initially incorrectly identified as Salvinia auriculata , was found almost worldwide in warm, tropical waters of all kinds; the first record was made in Sri Lanka in 1939. It is widespread worldwide and has been found in more than 55 tropical and subtropical, rarely warm-temperate, countries. Occurrences from South America, the presumed region of origin, were initially completely absent, so that an emergence is only considered possible in culture. Later the species was found in a region in the south of Brazil, in the states of Sao Paulo, Paraná, Santa Catarina and Rio Grande do Sul. It occurs here from the coast up to about 200 kilometers inland, up to an altitude of 500 meters. It is assumed that the drag is mainly due to transports, for example for the aquarium trade, with subsequent deliberate or unintentional release. The species is often mistakenly referred to as the common swimming fern under various names and used in aquariums.

In Europe, Salvinia molesta has already been registered in many countries in southern, western and central Europe, but is predominantly considered to be inconsistent. The situation in Germany is unclear, there are currently only finds for the Salvinia auriculata species aggregate that have not been assigned to one of the species.

Biology and ecology

The species only spreads to new waters through displacement, mostly by humans. Here it initially forms specimens with a long, brittle stem axis that serve to spread. Later, dense mats are formed that can cover the entire surface of the water. The species is very competitive and can effectively displace other floating plants, including species with a large spread such as thick-stemmed water hyacinth ( Eichhornia crassipes ) and water lettuce ( Pistia stratiotes ). The leaf area on the water surface doubled under optimal conditions in the greenhouse every 3.4 days, outdoors on the Kariba Dam in Africa every 8.1 days, on average under good conditions every 14 days. It can form mats up to one meter thick with a biomass of 250 to 600 grams per square meter. If other species take root in these mats, they can become impenetrable and paralyze boat traffic. Production was estimated at 45.6 to 109.5 tonnes of dry matter per hectare and year.

Salvinia molesta colonizes standing water, preferably disturbed or artificial water, but also penetrates natural habitats. It occurs in slowly flowing waters where it is confined to the shore region. The species is sensitive to dehydration, but can survive in the shade in wet mud for up to a year. She avoids brackish water habitats. It prefers nutrient-rich, mostly eutrophic , fully sunny and warm waters with water temperatures above 30 degrees, but it can grow between 10 and 40 degrees water temperature. It is quite sensitive to frost, buds of the species die at temperatures below −3 ° C.

Combat

Due to the negative ecological and economic effects, Salvinia modesta is considered an undesirable invasive species . An attempt is first made to prevent further spread, which is mainly caused by aquarists and the aquarium trade. Therefore, trade restrictions for the species now apply in numerous countries. In the European Union, keeping, breeding and trade has been prohibited since 2019, due to the inclusion in the list of invasive alien species of Union-wide importance ; restrictions were already in place in most member states.

The mass reproduction of the species outside of South America is mainly attributed to the lack of natural enemies there. For about 25 years, attempts have therefore been made to identify specialized herbivorous species that they can control. In addition to other tested species such as the grasshopper Paulinia acuminata and the borer Samea multiplicalis , weevils of the genus Cyrtobagous in particular proved to be effective antagonists. The importation of the species Cyrtobagous salviniae to Australia has led to a noticeable decline in swimming ferns there (control was made easier here because Australia has no native Salvinia species). The species later also contributed to biological control in the United States and Africa.

Individual evidence

  1. ^ DS Mitchell & PA Thomas: Ecology of water weeds in the neotropics. UNESCO Technical papers in hydrology 12, Paris 1972. 50 pages.
  2. ^ PJ Brownsey & LR Perrie (2015): Salviniaceae. In: Breitwieser, I .; Heenan, PB; Wilton, AD Flora of New Zealand - Ferns and Lycophytes. Fascicle 10. Manaaki Whenua Press, Lincoln. doi: 10.7931 / B1H59T
  3. ↑ M. Salas-Pascual & G. Quintana Vega (2016): Salvinia molesta DS Mitch. (Salviniaceae), nueva cita para Canarias y España. Botánica Macaronésica 29: 73-81.
  4. ↑ Pedro B. Schwartsburd & Cecília V. Miranda (2017): (2494) Proposal to reject the name Salvinia adnata (Salviniaceae). Taxon 66 (1): 202-203.
  5. ↑ Nathalie S. Nagalingum, Michael D. Nowak, Kathleen M. Pryer (2008): Assessing phylogenetic relationships in extant heterosporous ferns (Salviniales), with a focus on Pilularia and Salvinia. Botanical Journal of the Linnean Society 157: 673-685. doi: 10.1111 / j.1095-8339.2008.00806.x
  6. ^ SA Machado, AV Oliveira, TMC Fabrin, SMAP Prioli, AJ Prioli (2016): Molecular characterization of the species Salvinia (Salviniaceae) from the upper Paraná River floodplain. Genetics and Molecular Research 15 (3): gmr. 15038575.
  7. ^ A b c d J. Douglas Oliver (1983): A Review of the Biology of Giant Salvinia (Salvinia molesta Mitchell). Journal of Aquatic Plant Management 31: 227-231.
  8. ^ IW Forno & KLS Harley (1979): The occurrence of Salvinia molesta in Brazil. Aquatic Botany 6: 185-187.
  9. ↑ Salvinia auriculata agg., Species group small-eared floating fern Forum flowgrow (Aquasabi GmbH & Co. KG). accessed on March 25, 2020.
  10. ↑ a b European and Mediterranean Plant Protection Organization (editor) (2017): Salvinia molesta DS Mitch. Data sheets on pests recommended for regulation. EPPO Bulletin 47 (3): 531-536. doi: 10.1111 / epp.12 (open access)
  11. ↑ A. Hussner, K. von de Weyer, EM Gross, S. Hilt (2010): Comments on increasing number and abundance of non-indigenous aquatic macrophyte species in Germany. Weed Research 50: 519-526. doi: 10.1111 / j.1365-3180.2010.00812.x
  12. ^ IW Forno & AS Bourne (1984): Studies in South America of arthropods on the Salvinia auriculata complex of floating ferns and their effects on S. molesta. Bulletin of Entomological Research 74 (4): 609-621.
  13. ^ AA Calder & DPA Sands (1985): A new Brazilian Cyrtobagous Hustache (Coleoptera: Curculionidae) introduced into Australia to control salvinia. Journal of the Australian Entomological Society 24 (1): 57-64. doi: 10.1111 / j.1440-6055.1985.tb00185.x
  14. Jump up ↑ Philip W. Tipping, Melissa R. Martin, Ted D. Center, Tracy M. Davern (2008): Suppression of Salvinia molesta Mitchell in Texas and Louisiana by Cyrtobagous salviniae Calder and Sands. Aquatic Botany 88: 196-202. doi: 10.1016 / j.aquabot.2007.10.010
  15. ^ Arnold H. Pieterse, Marianne Kettunen, Sara Diouf, Ismael Ndao, Khady Sarr, Anne Tarvainen, Sandra Kloff, Seppo Hellsten (2003): Effective Biological Control of Salvinia molesta in the Senegal River by Means of the Weevil Cyrtobagous salviniae. Ambio 32 (7): 458-462 doi: 10.1579 / 0044-7447-32.7.458