Higher plant species


1831 Floating water-plantain    Luronium natans   
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Background to selection

Distribution of SACs with species 1831 Luronium natans.  Click image for enlarged map.
Distribution of SACs with species 1831 Luronium natans. Click image for enlarged map.

Description and ecological characteristics

 

Floating water-plantain Luronium natans occurs in a range of freshwater situations, including nutrient-poor lakes in the uplands (mainly referable to 3130 Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea) and slowly-flowing lowland rivers, pools, ditches and canals that are moderately nutrient-rich.

 

Luronium natans occurs as two forms: in shallow water with floating oval leaves, and in deep water with submerged rosettes of narrow leaves. The plant thrives best in open situations with a moderate degree of disturbance, where the growth of emergent vegetation is held in check. Populations fluctuate greatly in size, often increasing when water levels drop to expose the bottom of the water body. Populations fluctuate from year to year, and at many sites records of L. natans have been infrequent, suggesting that only small populations occur, in some cases possibly as transitory colonists of the habitat. Populations tend to be more stable at natural sites than artificial ones, but approximately half of recent (post-1980) records are from canals and similar artificial habitats. Its habitat in rivers has been greatly reduced by channel-straightening, dredging and pollution, especially in lowland situations.

European status and distribution

 

Luronium natans is endemic to Europe.

UK status and distribution Click to view UK distribution of this species

 

The ‘core’ natural habitat is considered to be lakes in Snowdonia and in mid-Wales, where Luronium natans has a very long and consistent history of occurrence. It appears to have spread eastwards along the canal system during the 19th century. It is absent from Northern Ireland but has recently been discovered in Ireland. It is probably also native to Cumbria, where a population survives. Elsewhere it occurs only as an introduction to ditches in the Norfolk Broads and to a few localities in Scotland, although some native populations may have formerly existed in Scotland. L. natans has been recorded in 40 10x10 km squares since 1980.

Site selection rationale

 

The selected sites include localities that are known to hold consistently large, naturally-occurring populations in lakes, rivers and heathland pools, as well as extensive populations in canals. Sites where conditions are considered to be particularly favourable to the species’ survival have been selected. Overall the site series provides representation of the species across its natural range in the UK and in a variety of ecological conditions.


Site accounts

Afon Eden - Cors Goch Trawsfynydd West Wales and The Valleys
Floating water-plantain Luronium natans is not especially abundant or strongly flowering in the Afon Eden but it does represent a rare and significant survival, and this population, scattered along ~100 m of meander pools, is an exceptional instance of the species’ growth in naturally slow-flowing waters.
Afon Gwyrfai a Llyn Cwellyn West Wales and The Valleys
Llyn Cwellyn and its outflow, the Afon Gwyrfai, support one of the largest and most diverse populations of floating water-plantain Luronium natans anywhere in Britain. There are extensive submerged, vegetative beds of this species in the clear, oligotrophic waters of the lake and (generally) several small flowering colonies around its edge whilst, downstream from the lake, L. natans occupies a highly unusual – and vulnerable – habitat along several hundred metres of slow-moving river. The diversity of growth forms and their range across the Cwellyn-Gwyrfai makes this an internationally significant site for the species.
Afon Teifi/ River Teifi West Wales and The Valleys
The Teifi is a mixed habitat supporting floating water-plantain Luronium natans at the western margins of its range in the UK. This species has been recorded in the nutrient-poor standing waters of the Teifi pools in the headwaters of the river. It has also been recorded in a moderately nutrient-rich stretch of the river immediately downstream of Cors Caron.
Brown Moss Shropshire and Staffordshire
Brown Moss is an area of former heathland, now largely colonised by woodland, with a series of shallow pools. Floating water-plantain Luronium natans has been known to occur at Brown Moss for several years, and this site possibly represents a relict natural lowland population of the species. The population of Luronium at Brown Moss is relatively small, and appears to behave as a metapopulation, colonising the various pools according to their suitability.
Cannock Extension Canal Shropshire and Staffordshire, West Midlands
Cannock Extension Canal in central England is an example of anthropogenic, lowland habitat supporting floating water-plantain Luronium natans at the eastern limit of the plant’s natural distribution in England. A very large population of the species occurs in the Canal, which has a diverse aquatic flora and rich dragonfly fauna, indicative of good water quality. The low volume of boat traffic on this terminal branch of the Wyrley and Essington Canal has allowed open-water plants, including floating water-plantain, to flourish, while depressing the growth of emergents.
Elenydd East Wales, West Wales and The Valleys
The remote Elenydd lakes are amongst the best upland oligotrophic lakes in Wales and have been relatively untouched by abstraction and water-level modification. Their populations of floating water-plantain Luronium natans show a highly natural submerged distribution, in association with a wide range of associated species, and are an apparently ancient refuge site secure from the intensification which has afflicted lowland populations.
Eryri/ Snowdonia West Wales and The Valleys
Snowdonia in north Wales is an example of a montane lake habitat supporting floating water-plantain Luronium natans. Records date back to the 18th century, indicating that habitat conditions are particularly favourable for this species.
Montgomery Canal East Wales
This is the largest and the most extensive population of floating water-plantain Luronium natans in Britain and is a highly significant lowland population. In favourable management conditions the species can be dominant over kilometre lengths of canal, carpeting the shallow bed and flowering and setting seed in abundance. This is a semi-natural population, having colonised from drift material or seed but needing periodic human disturbance for continued growth; in this respect the canal is a substitute for the species’ former slow-moving, mesotrophic river niche, which has been largely destroyed in lowland Britain.
North West Pembrokeshire Commons/ Comins Gogledd Orllewin Sir Benfro West Wales and The Valleys
Floating water-plantain Luronium natans in Pembrokeshire is relatively isolated from its central and north Wales population centres and it occupies a distinctive – and now highly relict – habitat here, in heathland pools. The species was recorded at Dowrog in the early 19th century but it has only recently been rediscovered, following extensive remedial management. Here, in shallow rain-fed pools, it flowers and sets seed prolifically, almost certainly enabling colonisation of transient habitat elsewhere.
River Dee and Bala Lake/ Afon Dyfrdwy a Llyn Tegid Cheshire, East Wales, Shropshire and Staffordshire, West Wales and The Valleys
Species occurrence account not yet available.
River Derwent and Bassenthwaite Lake Cumbria
This site represents the northern limit of floating water-plantain Luronium natans in the UK, and its occurrence in relatively shallow, oligo-mesotrophic lakes. Within the site, the species is found in two lakes, Derwent Water and Bassenthwaite Lake. Both of these lakes have healthy populations of the species in extensive, species-rich beds of aquatic macrophytes. In Bassenthwaite Lake it also occurs on muddy lake-shores. These are the only two known sites for Luronium in the Lake District.
Rochdale Canal Greater Manchester
Rochdale Canal supports a significant population of floating water-plantain Luronium natans in a botanically diverse waterplant community which also holds a wide range of pondweeds Potamogeton spp. The canal has predominantly mesotrophic water. This population of Luronium is representative of the formerly more widespread canal populations of north-west England.
St David`s / Ty Ddewi West Wales and The Valleys
The two larger pools – and one tiny satellite – on Ramsey Island are an internationally significant site for floating water-plantain Luronium natans, providing ideal habitat for the species in its flowering, near-annual form. Rain-fed lowland pools, usually in heaths, are now an exceptionally rare habitat, and the population here is maintained by a combination of excellent management, favourable topography and clean rain.

SACs where this Annex II species is a qualifying feature, but not a primary reason for site selection

Rhinog West Wales and The Valleys
 

Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.