Luronium natans (floating water-plantain)
Floating water-plantain is an unusual aquatic plant, rare in the UK, with a differing leaf structure depending on the depth of water in which it grows, and showy white flowers.
Luronium natans (Photo: Annette Hoeggemeier)
Found mainly in lakes and canals with a fairly acid pH level.
About this species
Floating water-plantain is found in two different forms. In shallow water, it develops floating oval leaves, while in deep water it can have long narrow, strap-shaped leaves.
When not flowering, its variable leaf-shape makes it easily confused with other related plants such as Alisma plantago-aquatica (water-plantain) or Echinodorus ranunculoides (lesser water plantain). Luronium natans has even been confused with the common terrestial species Plantago major (greater plantain) as it occasionally grows in damp grassland.
It is one of the most protected species in the UK, ensuring Special Area for Conservation status for any locality in which it occurs. Nevertheless it does seem to be gradually increasing its distribution in the UK.
Geography and distribution
Luronium natans is restricted to Europe, and is found scattered across western Britain, with records in Wales, the West Midlands and northern England. It has also been introduced to some water-bodies in the Norfolk Broads and a few areas in Scotland.
Floating water-plantain seems to have spread eastwards from its 'home' territory of North and mid-Wales, in particular Snowdonia, as a result of the building of the canal systems in the 19th century. Many recent records of Luronium natans have been from canals.
Floating water-plantain is a member of the aquatic plant family Alismataceae. It has a highly variable leaf structure ranging from oval to strap-shaped leaves, 3-petalled flowers and a fruiting head of hemispherical achenes. The flowers usually occur singly, on long stems from the leaf joints, and are white with yellow spots at the base of the petals.
Floating water-plantain seems to flourish best where the water is open, and where there is some disturbance. It does not seem to be able to tolerate competition from other aquatic vegetation, and populations fluctuate considerably in size as a result of dredging operations, or when the water levels drop to expose the bottom. In spite of the fact that over half of the recent (post-1980) records for this species have been from canals, plant populations seem to be more stable in natural sites than in artificial ones, such as canals and similar habitats.
Threats and conservation
Luronium natans is listed under Annexes II and IV of the Habitats Directive, Appendix I of the Bern Convention, Schedule 4 of the Conservation (Natural Habitats, etc.) Regulations 1994, and Schedule 8 of the Wildlife and Countryside Act, 1981.
The threat to this plant comes mainly from the opening up of the canals to leisure craft, which stir up the mud and ooze, increasing the turbidity of the water. In rivers, its preferred habitat has been reduced greatly by straightening of channels, dredging and pollution.
L. natans is listed in the UK Biodiversity Action Plan (UK BAP), and is included in English Nature's Species Recovery Programme. There are a number of organisations involved in protecting the future of this plant, including the Countryside Council for Wales, and British Waterways who are the lead partner. Amongst the measures proposed are the provision of 'sanctuary' areas of the canal, protected by piling, where the floating water-plantain can grow without excessive disturbance and where the turbid water stirred up by boat traffic will not cause harm. It has also been proposed that where canal restoration might involve damage to the plant populations, reserves should be created for L. natans so that it can be re-introduced following completion of the engineering work.
Luronium natans is grown as an ornamental aquatic plant.
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
Number of seed collections stored in the Millennium Seed Bank: One
Germination testing: Unsuccessful
Brickell, C. (1989). Gardener’s Encyclopedia of Plants and Flowers. Dorling Kindersley, London.
Kew Science Editor: David Simpson
Kew contributors: Sustainable Uses Group
Copy editing: Kew Publishing
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