Northern Ireland's Priority Species

Sium latifolium – greater water-parsnip

Sium latifolium

Sium latifolium L.
Family: Apiaceae

Previously this large umbellifer was widespread and typical of very wet, marshy waterside vegetation in Britain and Ireland, but it suffered a catastrophic decline during the last 200 years and has become scarce over much of its range.

In brief

  • Greater water-parsnip is extremely frequent and abundant in Fermanagh around Upper Lough Erne

  • It grows in wet ditches on species-rich fens and swamps, typically in a floating mat of vegetation on the margins of large lakes and rivers

  • It prefers still or slow-moving, shallow water that is not acid, and where the soil is formed from sedge peat, or has been deposited by rivers

  • It can tolerate the light shade of accompanying reeds and bulrushes, but cannot cope with the deeper shade of wet woodland species, for example, alder, ash and willow, if this encroaches

  • It flowers in July and August

  • It is a UK Priority Species

  • Cattle and other stock seem to be immune from the plant's poison, but dairy cows are discouraged from browsing it since it gives an unpleasant taste to their milk

  • The plant can survive moderate browsing and trampling by cattle. However drainage and excessive mechanical cleaning of waterways can kill it

  • WARNING: this plant is deadly poisonous and contact with it should be avoided at all times.

Species description
Greater water-parsnip is a robust, bright green, hairless, perennial which can grow up to 2m tall in shallow, sheltered, often still water. The stem is hollow and grooved and the leaves, which can grow to 30cm, have stalks which are also hollow and which clasp the main stem. The flowers are white, measure about four millimetres across, and are carried on an umbel (like the ribs of an umbrella), characteristic of this family of plants.

Life cycle
Greater water-parsnip is a perennial, its flowers appearing in July and August. Seeds germinate underwater and the plant produces finely-divided, submerged leaves. It also overwinters underwater, so there is absolutely no doubt that it is a member of our true aquatic flora, rather than an emergent terrestrial species (Cook, 1998). Greater water-parsnip can compete with and tolerate the shade of other tall emergent herbs including reeds (Phragmites) and bulrushes (Typha), but it becomes shaded out if wet woodland (that is, swampy fen-carr ) is allowed to develop.

Similar species
The only other umbellifer relative of similar size in this wetland habitat is Cicuta virosa, Cowbane. Amongst other differences, it has much narrower, more finely-cut leaf segments, so the two plants could not readily be confused, even when only in leaf.

How to see this species
The plant is frequent and locally abundant in wet, marshy ground all round Upper Lough Erne, County Fermanagh. It flowers in July and August. Relevant access permissions should always be sought prior to visiting any sites.

Current status
Greater water-parsnip is extremely frequent and abundant in Fermanagh around Upper Lough Erne, and it is likely to be its current stronghold in the British Isles. In England it is still found in fair numbers south and east of a line drawn between the River Humber and the Bristol Channel. It is found across most of Europe although it is rare near the Mediterranean region.

Why is this species a priority in Northern Ireland?

  • Listed as a UK Priority Species

  • It is scarce and in decline

Threats/Causes of decline
Tall-herb fen vegetation grows in a sensitive aquatic habitat which has recently suffered major decline across much of Britain and Ireland due to drainage and pollution. Greater water-parsnip does not like disturbance and cannot survive regular cutting or ditch clearance. It can only tolerate very occasional dredging or reshaping of its ditches, and moderate levels of grazing and trampling. The neglect of ditches, allowing scrub and young woodland to invade and become established will also kill off the plant. Even in conservation protected sites, decline has been observed and new plants are rare (Stewart et al. 1994).

Conservation of this species

Current action
There is a UK Species Action Plan which was written in 1998.

  • A large proportion of the Northern Ireland population is protected by ASSI / SPA / SAC status at Upper Lough Erne

  • Implementation of the Northern Ireland Habitat Action Plan for Fens, Reedbeds and Floodplain Grazing Marsh.

Proposed objectives/actions

  • Maintain the range of greater water-parsnip

  • Ensure that viable populations are maintained at all extant sites

  • Achieve the spread of greater water-parsnip from extant sites.

What you can do
Records of new sites for this plant elsewhere in Ireland and estimates of the size of populations are always valuable. Send to: The Botanical Society of the British Isles – 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, [at]

Further information

Flora of Northern Ireland

Northern Ireland Habitat Action Plans

Cook, C.D.K. (1998). Watsonia 22: 119-120. Book review of – Aquatic plants in Britain. By C.D. Preston and J.M. Croft. Harley Books, Colchester. 1997.

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

Stewart, A., Pearman, D.A. and Preston, C.D. (1994). Scarce Plants in Britain. Joint Nature Conservancy Committee, Peterborough.

Text written by:
Dr Ralph Forbes