Northern Ireland's Priority Species

Eleocharis parvula – dwarf spike-rush

 

Distribution map

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Eleocharis parvula (Roemer & Schultes) Link ex Bluff
Family: Cyperaceae

This is a tiny plant that inhabits a seldom visited habitat — slightly brackish mud. Since its first discovery in Ireland it has only been recorded from three sites, of which the only place that it remains is the Bann Estuary in County Londonderry.

In brief

  • Very specific to bare mud flats at around the limit of tidal influence
  • Seldom flowers, but can spread vegetatively
  • The only place it grows in Ireland is the Bann Estuary from where it has been long known
  • Only known from a handful of sites in the UK which makes the Bann population all the more important
  • Best time to look for it is the summer
  • Sensitive to dredging and reclamation.

Species description
Taxonomically, spike-rushes reside within the sedge family. It would be fair to say that spike-rushes in general are not showy or spectacular species. Dwarf spike-rush (Eleocharis parvula), in particular, is not likely impress. Although one of Belfast’s eminent naturalists, Arthur Wilson Stelfox, was prompted in 1926 to describe it as a ‘charming little plant’, at 2 to 6cm tall this diminutive plant is easy to overlook, especially as it grows on mud flats where it is often clothed in algal filaments. The stems are without leaves so the plant has the appearance of a tuft of little green needles protruding from the mud surface. It rarely flowers, but if you are lucky enough to see them, the spikelets comprise a mass of flower scales forming a dull brown oval about 3mm long.

Life cycle
Dwarf spike-rush inhabits slightly brackish mudflats close to the upper limit of tidal influence along a river/estuary side and spreads by runners in the surface layers of mud. The runners form tiny elongated bulbils which become established as new and separate plants once the grass-like leaves are formed and the runner has withered. This happens over the course of the summer. In late August to early October, tiny dark oval flowers may be produced, and the seeds set to germinate the following year; however, it is known to be a very shy flowerer and some years may not do so at all. The main body of the plant does not survive the winter, but any seeds and some of the bulbils remain dormant and viable. The principle mechanism by which the plant spreads is thought to be the movement of floating vegetative fragments by tidal action.

Similar species
It can be confused initially with seedlings of other grass-like species of similar habitats, such as saltmarsh rush (Juncus gerardii). The bulbils and slender white rhizomes separate dwarf spike-rush from seedlings of other plants. There is another tiny spike-rush — needle spike-rush (Eleocharis acicularis), which inhabits the muddy margins of lakes, especially in the Erne basin, but it does not stray into the brackish habitats to which dwarf spike-rush is confined.

How to see this species
The only extant Irish record is from the mouth of the River Bann in County Londonderry, discovered in 1937 by the celebrated Holywood-born naturalist Robert Lloyd Praeger. It is important to look for the plant in summer, but it does not much matter whether it is flowering or not.

Current status
This species was first recorded in the island of Ireland by A.G. Moore in 1868 in County Wicklow. Here, and in a subsequently discovered location in County Kerry, it is known to have disappeared and dwarf spike-rush is considered extinct in the Republic of Ireland. Now it is only known from the Bann estuary where it has remained since it was first recorded there by Praeger. Apparently known from both sides of the river.

All wild plants are given some measure of protection in Northern Ireland under the Wildlife (NI) Order, 1985. But dwarf spike-rush is amongst the fifty-six species, listed in Schedule 8 which are afforded special protection. Thus it is illegal without a licence to pick intentionally, uproot or destroy the plant, or to collect the flowers or seeds.

Why is this species a priority in Northern Ireland?

  • Rare, confined to a small population of one or two sites in Northern Ireland with Northern Ireland being a stronghold and with the Irish population restricted to Northern Ireland
  • It is listed in the Irish Red Data Book as Endangered.

Threats/Causes of decline
It was lost from its former Republic of Ireland sites due to river (and canal) engineering.

Conservation of this species

Current action

  • The only known site for this species is within the designated Bann Estuary ASSI/SPA
  • Implementation of the Northern Ireland habitat action plan for Mudflats, although this relates more to zoological than botanical heritage.

Proposed objectives/actions

  • Maintain the number of viable populations of the species.

What you can do
This is not a species that is likely to be found unless it is searched for. Check mud surfaces along creek margins and in tidal pans in river mouths and estuaries close to the upper influence of saline water. The River Foyle would seem a good place to start. Care must be taken not to destroy or uproot any plants should this species be found. But the site location and an estimate of the extent of the patches (for it is a gregarious species) should be noted and reported to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU, Tel: 028 9039 5256 or email cedar.info [at] magni.org.uk.

Further information

Links
Mudflats Action Plan

Information on ASSIs

Flora of Northern Ireland

Literature
Praeger, R.L. (1937). Scirpus nanus (=Eleocharis parvula) in the Bann Estuary. Irish Naturalists’ Journal 300-301.

Text written by:
Shaun Wolfe-Murphy