Cicuta virosa

Taxonomy 

Cicuta virosa L. has no synonyms (Stace, 1997), although the English name for it, Cowbane, is sometimes used in America for the related species Cicuta maculata L.

Chromosome No.: 2n = 22 (Stace 2010).

Cicuta virosa

Photography: A.J.Lockton

Distribution 

It has a curiously patchy distribution in the British Isles. The main centre of population is in central Ireland, and it is also quite common in the Shropshire-Cheshire plain; but only rare and scattered elsewhere. It is widespread throughout northern parts of Eurasia as far east as Japan (Braithwaite 1994).

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Status 
  • Origin: native.
  • Rarity: in Britain it is Nationally Scarce (present in fewer than 100 hectads).
  • Threat: the population appears stable (Preston, Pearman & Dines 2002) after a decline in the 18th century (ibid.). Braithwaite (1994) suggests that it has been eliminated from some sites because of the harm it can cause to livestock.
  • Conservation: several counties list it as an axiophyte, and it seems likely that it would be considered one in any county in which it occurs.
Ecology 

Braithwaite (1994) described C. virosa as ‘an aquatic species of lake shores, pond margins, mires and ditches’, but Preston & Croft (1997) did not consider it an aquatic plant. It has an Ellenberg Value for wetness of 9 on a scale from 1-12 (Hill et al., 1999) so, strictly speaking, it is best described as a wetland plant. Rodwell (1991; 1995) lists it as a component of W5 Alnus glutinosa woodland, of S4 & S24 Phragmites australis reedbeds, and of S7 Carex acutiformis & S12 Typha latifolia swamps. Braithwaite (op. cit.) says it grows in shallow water or on a floating mat of vegetation. A photograph on this page shows it in the latter situation - on a mat of Menyanthes trifoliata floating in Shrawardine Pool in Shropshire. It is a plant of circumneutral pH, often occurring on organic, peaty soils but not on acid mires.

Toxicity: All parts of Cowbane are poisonous to humans and livestock, and Braithwaite (1994) claims that it is frequently fatal to cattle. However, it often occurs in grazed fens and it is not difficult to find stories of it being grazed by cattle with no apparent harm. The reason for this is that it is the roots that contain the highest concentrations of cicutoxin, so unless these are exposed there may be no ill effects.

Further Work 

The pattern of distribution of Cowbane is unusual, and none of the published accounts offers an explanation. Losses seem to have occurred mainly in populations isolated from its core range - was this the end point of a lengthy decline, or just transitory occupation of unsuitable habitat? Little is known about its lifecycle and ecology. It may be one of those plants that is associated with fluctuating water levels - a habitat type that has been largely overlooked by British ecologists and conservationists. Research into the importance of exposed substrate in its reproduction might prove worthwhile.

References 
  • Braithwaite, M.E. 1994. Cicuta virosa L. In Stewart, Pearman & Preston, Scarce Plants in Britain, p. 114-115.
  • Hill, M.O., Mountford, J.O., Roy, D.B., & Bunce, R.G.H. 1999. Ellenberg’s indicator values for British plants. HMSO.
  • Preston, C.D. & Croft, J.M. 1997. Aquatic Plants in Britain and Ireland. Harley Books, Colchester.
Citation 
Lockton, A.J. (date accessed). Species account: Cicuta virosa. Botanical Society of the British Isles. www.bsbi.org.uk.

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