Ribbon-leaved water-plantain (Alisma gramineum)
|Size||Submerged parts: up to 1 m|
Emergent parts: up to 40 cm
Classified as Vulnerable in Europe. Classified as Critically Endangered in the UK.
The aquatic ribbon-leaved water plantain resembles its more common relative, common water plantain; however it is generally more diminutive in all dimensions, has aerial leaves that are not heart-shaped at the base and submerged leaves that are long and ribbon-like. The plant may however be identified with certainty by its styles which are strongly curved back. The small, three-petalled flowers are white or pale pink with a yellow spot at the centre, are about 5-7 mm across and grow in a many-branched head with an average of about 60 flowers but up to 300. The species is also easily mistaken for another close relative, the narrow-leaved water-plantain, and these two were originally thought to be varieties of the common water-plantain.
The plant occurs in cold temperate latitudes across Europe, Asia and North America but is thought to be uncommon throughout its range. In the UK it is found at two sites. One is a shallow lake in Worcestershire where it has been known for years, and the other is a drainage channel in Lincolnshire where it was rediscovered in 1991. It has disappeared from the only two other sites where it was formerly recorded, one in Cambridgeshire and the other in Norfolk.
Ribbon-leaved water-plantain may grow as a deeply submerged aquatic but also occurs in shallow waters and on mud around the margins of lowland lakes, rivers, ponds and ditches. It requires nutrient-rich conditions (described as eutrophic) but cannot tolerate competition from other plants and tends to occur in open habitats.
The species is a short-lived perennial, although it often behaves as an annual. The leaves can develop both below water and above the surface and the flowers appear from June to September. The plant has the ability to self-fertilise and can produce a large quantity of seed.
Successful germination may rely on freezing, the disturbance of the mud in which the seed falls or other factors; however it has been found that seeds can survive dormant for at least a few years until conditions become suitable for germination.
The reason for this plant's rarity in the UK is not fully understood. Its loss from two of its former sites may be attributed to changes in management and the subsequent development of competing vegetation. On the continent, it may occur in abundance in groups of suitable shallow water-bodies that are linked by factors such as the movement of herbivorous animals such as wild boar or by the variable flow of rivers. It is thought likely that one of the reasons the species is rare in the UK is because such dynamic processes are no longer generally available to the species. Alternatively, the plant may have always been very rare here.
Being an inconspicuous plant, it is also possible that populations have been overlooked in some areas, particularly in deep waters.
In partnership with the Environment Agency - the government body responsible for pollution prevention and control in England and Wales, and for the management and use of water resources including flood defences, fisheries and navigation - English Nature has produced a Species Action Plan (SAP) for this plant. As part of English Nature's Species Recovery Programme, survey and monitoring work has been carried out to discover more about the conditions required by the ribbon-leaved water plantain.
As well as looking at ways to manage the sites where the plant is currently found, plans to re-introduce it to former sites have been investigated. The single known site in Norfolk lies in the area known as Breckland, where the species has been recorded once in one of the ephemeral meres. The Breckland meres are bodies of shallow water that rise and fall annually with the ground-water table.
When the water level has been low in these meres, the soil bed has been disturbed in places by rotovation. It is hoped that by creating this disturbance, dormant seed may be stimulated to germinate and the plant re-appear.
Other possible sites to experiment with managing this species have been investigated and seed from the Millennium Seed Bank at Wakehurst Place, part of the Royal Botanical Gardens, Kew, have been germinated in nursery conditions. If natural regeneration programmes prove unsuccessful, cultivated plants will be introduced into suitable sites and new populations established.
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- Annual: lives or grows for just one year.
- Eutrophic: nutrient enrichment of aquatic or terrestrial ecosystems.
- Perennial: plants that live for at least three seasons; after an initial period they produce flowers once a year.
- Styles: an elongated part of the female reproductive organs of a flower that bears the stigma (the receptive area where pollen germinates), usually at its tip. (see http://www.rbgkew.org.uk/ksheets/pdfs/flower.pdf for a fact sheet on flower structure)