Ranunculus fluitans – river water-crowfoot
Ranunculus fluitans Lam.
Family: Ranunculaceae
River water-crowfoot is the rarest of all the water-crowfoots (Ranunculus Subgenus Batrachium) in Ireland, being restricted to the Six Mile Water, County Antrim.
In brief
- Found only in a single stream in Ireland – the Six Mile Water
- Best seen in flower (about July)
- Rare, with the Irish population restricted to Northern Ireland
- Threatened mainly by water pollution.
Species description
The leaves of this species are long and finely divided into long ‘capillary’ segments, which are always submerged in the water and are aligned along the direction of the stream flow. The flowers are small (approx 15 to 25mm or up to approx 0.75 to 1 inch diameter), with 10 or rather fewer white petals, yellow stamens and small green sepals; they are carried just above water level. One-seeded dry fruits break away from the old flower stalk when mature.
The Irish plants appear to be rather untypical in leaf length compared to populations in England and Scotland.
Life cycle
Flowering is from about late May to August. The fruits are dry and one-seeded (called achenes – they are identical to those produced by buttercups) and are easily distributed by water, birds or wind, although nothing is known of just how effective seed dispersal is in the Six Mile Water population. Since hybrids with other species occur in the river, sexual reproduction seems to play some part in maintaining the population.
Similar species
It can be easily confused with three other similar plants: the very common stream water-crowfoot (R. penicillatus (Dumort.) Bab, the pond water-crowfoot (R. peltatus Schrank) and sterile hybrids between river and pond water-crowfoots (R. x kelchoensis S.D. Webster - the so-called 'Kelso water-crowfoot'), all of which are known to occur in the Six Mile Water, County Antrim. Unlike any of these three, river water-crowfoot has only submerged leaves — the others also have aerial or terrestrial leaves, or 'transitional' leaves.
River water-crowfoot's other distinguishing features in the Six Mile Water population are its generally smaller flowers compared to the other water-crowfoots; 7-10 petals, instead of 5; longer submerged leaves (up to approx 30cm or 12 inches - i.e. not very much longer than some forms of the stream water-crowfoot); more rigid leaf segments in the submerged leaves.
How to see this species
It can be found most easily where the river is fairly shallow and rapid-flowing, for example, at Dunadry Bridge. It is best seen when in flower which is around July. It is often accompanied by stream water-crowfoot (R. penicillatus (Dumort.) Bab). Relevant access permissions should always be sought prior to visiting any sites.
Current status
It is confined to the Six Mile Water, County Antrim between the Six Mile Water Bridge at Templepatrick and the river's mouth at Lough Neagh. It is protected under the Wildlife Order (NI) 1985.
Why is this species a priority in Northern Ireland?
- It is rare with the Irish population restricted to Northern Ireland. The only Irish population is that of the Six Mile Water, County Antrim.
It is an Irish Red Data Book Species, classed as Rare.
Threats/Causes of decline
The plant was lost from the part of the Six Mile Water above Templepatrick at some time prior to 1883 — almost certainly the result of documented pollution from a waterside factory.
The main threat to the remaining population is also probably water pollution, especially the sort which causes cloudy water conditions such as eutrophication from agricultural run-off or sewage.
Conservation of this species
Current action
There is a Northern Ireland Species Action Plan which was published in 2005.
- EHS has produced a River Conservation strategy for Northern Ireland (DOE, 2001) outlining its role and responsibility in protecting, conserving and enhancing the natural and built heritage values of rivers in Northern Ireland and facilitating their sustainable use.
Proposed objectives/actions
- Maintain the current populations of river water-crowfoot along a 12km length of the Six Mile Water
- Ensure that all known sites are managed in a manner that is beneficial to the conservation of river water-crowfoot
- Ensure that all organisations responsible in the water management of the Six Mile Water are aware of the potential risks to river water-crowfoot that could be caused through inappropriate water management
- Provide advice to land owners with river water-crowfoot on their land about suitable management requirements of the species
- Establish the distribution, abundance and viability of the species
- Research the ecology and genetics of the species to determine the origin of the species and to further understand its presence and ecological requirements in Northern Ireland.
What you can do
You can help in monitoring the health of the Six Mile Water river water-crowfoot population by sending records of the species to The Botanical Society of the British Isles (BSBI), c/o Botany Department, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU or to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU, Tel: 028 9039 5256, CEDaR.info [at] nmni.com.
Further information
Links
Northern Ireland Species Action Plan for river water-crowfoot
River Conservation Strategy for Northern Ireland (2001)
Literature
Beesley, S. (2006). County Antrim Scarce, Rare and Extinct Vascular Plant Register. Ulster Museum. Belfast.
Curtis, T.G.F and McGough, H.N (1988). The Irish Red Data Book – 1 Vascular Plants. Stationery Office, Dublin.
Hackney, P. (1992). Stewart and Corry’s Flora of the North-east of Ireland, 3rd edn. Inst. Of Irish Studies, Belfast.
Text written by:
Paul Hackney
iNaturalist: Species account : iNaturalist World Species Observations database