Northern Ireland's Priority Species

Ruppia cirrhosa – spiral tasselweed


Distribution map

Click here to view an interactive map of the Northern Ireland dataset as currently collated by CEDaR.
The map is generated through the NBN Gateway using their Interactive Mapping Tool.


Ruppia cirrhosa (Petagna) Grande
Family: Ruppiaceae

Spiral tasselweed is a visually unimpressive submerged aquatic species of saline ponds and lagoons.

In brief

  • Found at a number of sites on the coasts of Counties Down, Antrim and Londonderry

  • Found in brackish (saline) water bodies, often associated with the similar beaked tasselweed (Ruppia maritima)

  • Best seen when in fruit in late summer or autumn

  • Northern Ireland holds about 50 per cent of the total number of Irish sites and the species appears to be rare and declining

  • Threatened by water pollution or drainage of sites.

Species description
It is an easily-overlooked submerged aquatic plant with extremely fine, slender stems and leaves and tiny flowers. The fruits are also tiny, about 2mm long, on long stalks attached to a common peduncle (main flowering-stem) which is long and tends to grow into a spiral.

Life cycle
Both tasselweed species are perennial, with slender rhizomes rooted in mud. There appears to be little information on the details of the biology or life cycles of these species. Dispersal of the plants is probably by transfer of portions of plant by birds and dispersal of fruits in water or by birds. Whether plants die down during winter may depend on the temperatures prevailing during a particular season.

Similar species
Very similar to beaked tasselweed from which it cannot be reliably distinguished unless in fruit. Beaked tasselweed has a short, straight peduncle; spiral tasselweed has a long spiral peduncle The two species often occur together, but beaked tasselweed can grow in much shallower water, even on the mud of saltmarshes where it can accompany eelgrass (Zostera spp.)

How to see this species
Sites where this species has been seen in recent years include Victoria Park in Belfast, lagoons by Larne Lough near Glynn and drainage ditches behind the sea walls at Myroe, Donnybrewer by Lough Foyle and Strangford Lough, for example, Anne’s Point. The plant is often mixed in with other brackish-water aquatics such as fennel pondweed (Potamogeton pectinatus) and horned pondweed (Zannichellia palustris). It is best seen when it is in fruit in late summer or autumn. Relevant access permissions should always be sought prior to visiting any sites.

Current status
It is recorded from brackish waterbodies on the coast of Lough Foyle, saline lagoons adjacent to Larne Lough, and various creeks and ponds adjacent to the County Down shore of Belfast Lough and Strangford Lough; also in the River Quoile.

Why is this species a priority in Northern Ireland?

  • The species appears to be rare and declining

  • Northern Ireland holds about 50% of the total number of Irish sites.

Threats/Causes of decline
The principal threats are destruction of the sites by drainage, infilling, or pollution. Several sites are artificial water bodies such as drains or the lagoons at Larne Lough which were created by construction of the loughside railway line, and are probably not generally perceived as sites of great amenity or conservation value.

Conservation of this species

Current action

  • Saline lagoons are the subject of UK and Northern Ireland Habitat Action Plans

  • Coastal lagoons are listed as a priority habitat on Annex 1 of the EC Habitats Directive

  • Coastal lagoons are listed as an interest feature in the Strangford Lough SAC

  • A total of 16 saline lagoons occur in designated sites including ASSIs, SPAs, SACs and Ramsar sites. Lough Foyle ASSI and SPA include some saline lagoon habitat.

Proposed objectives/actions

  • Maintain saline lagoons containing spiral tasselweed

  • Maintain the condition of saline lagoons and their associated plant and animal communities including spiral tasselweed

  • Create lagoonal habitat to offset losses.

What you can do

Further information

Pictures of Isle of Skye Ruppia cirrhosa

Pictures of Isle of Skye Ruppia maritima

Northern Ireland Habitat Action Plan for Seagrass Beds

Northern Ireland Habitat Action Plan for Saline Lagoons

UK Habitat Action Plan for Saline Lagoons


Text written by:
Paul Hackney