Northern Ireland's Priority Species

Hottonia palustris – water-violet

 

Distribution map

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Hottonia palustris L.
Family: Primulaceae

Water-violet is an attractive aquatic plant known since 1810 from the area around Crossgar – Inch – Downpatrick, but now confined to one site in the marshes near Downpatrick, County Down, where it is considered to be probably native. Despite its common name it is a member of the primrose family.

In brief

  • Now only known from a swampy woodland near Downpatrick, County Down

  • Flowers in May and June

  • The County Down site is thought to be the only native Irish population

  • Drainage of the site or nutrient-enrichment of the water are potentially the greatest threats to its survival. Either may account for the past loss of other sites nearby

  • A few other Irish sites are known, but all are considered to be introductions.

Species description
A floating or rooted aquatic perennial with whorls of finely divided submerged leaves and producing an erect spike of lilac-coloured flowers, each with a yellow 'eye', in May to June.

Life cycle
The flowers of water-violet are heterostylous, like primroses and other members of the same family. This means that there are two sorts of plants each with one kind of flower, known as pin and thrum, distinguished by having a long or short style respectively – a feature which encourages cross-fertilisation by insect visitors seeking nectar. Seeds are produced in a capsule which splits open when mature. The plants also spread vegetatively by means of stolons which is reported in some areas of its range to produce colonies which are totally composed of pin or thrum type and which consequently set few seeds. The extent to which this may happen in the Northern Ireland population has not been investigated.

Similar species
There are no similar species with which this could be confused.

How to see this species
Water-violet is found in Hollymount Forest NNR near Downpatrick, in drainage ditches inside a very wet, swampy willow-alder woodland. It flowers during May and June. The warden must be contacted before visiting.

Current status
Water-violet is now confined to one site, Hollymount Forest NNR, near Downpatrick, County Down. This site is thought to have the only native Irish population. A few other Irish sites are known, but all are considered to be introductions. It is protected under the Wildlife Order (NI) 1985. Outside Ireland, it occurs in Great Britain and Northern and Central Europe eastwards to Siberia.

Why is this species a priority in Northern Ireland?

  • This species is rare – Northern Ireland holds the only Irish population which is believed to be native.

Threats/Causes of decline
Up to 1921 this species was known from a small number of sites in the area between Crossgar and Downpatrick. The reasons for the loss of these other sites is not known precisely, but is likely to have been because of vegetation clearance, drainage, water-enrichment or trampling by cattle. The remaining population within the Hollymount Forest NNR is now unlikely to be affected by such factors.

Conservation of this species

Current action

  • Its remaining site is protected as a NNR

  • It is regularly monitored by EHS

  • Implementation of the Northern Ireland Habitat Action Plan for Wet Woodland.

Proposed objectives/actions

  • Maintain the viability of the remaining population

  • Maintain appropriate management of the site.

What you can do
Records of the extent of the population and numbers of individuals are always useful as well as more detailed observations such as seed-set, insect visitors, proportions of pin/thrum plants etc. Send these to The Botanical Society of the British Isles c/o Department of Botany, 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 5251 or Email: cedar.info [at] magni.org.uk.

Further information

Links
Flora of Northern Ireland

Hollymount Forest NNR

Northern Ireland Habitat Action Plans

Literature
Hackney, P. (1992). Stewart & Corry’s Flora of the North-east of Ireland. 3rd Edition. Inst. of Irish Studies, Belfast.

Preston, C.D., Pearman, D.A. and Dines, T.D. (2002). New Atlas of the British & Irish Flora. Oxford University Press.

Text written by:
Paul Hackney