Cicuta virosa L., Cowbane
Account Summary
Native, common and locally abundant. Eurasian boreo-temperate, but part of a circumpolar species complex.
1726-72; Anon (C. Threlkeld); Co Fermanagh.
April to November.
Growth form and preferred habitats
This robust, tall, glabrous, much branched perennial umbellifer has hollow stems 0.5-1.5 m high, often streaked with purple. It grows from a somewhat misshapen globose, rootstock or rhizome that is developed at ground level and has short, narrow roots growing from its base. Leaves are 2- to 3-pinnate, the lobes 3-9 cm linear-lanceolate, remotely and deeply serrate (Tutin 1980; Mulligan & Munro 1981; Jonsell & Karlsson 2010). The only other large aquatic, white-flowered umbellifer with which C. virosa might be confused is Sium latifolium (Greater Water-parsnip), which differs in having simply pinnate leaves and umbels with leafy bracts (NB both these species have small, linear bracteoles at the base of the ultimate subdivisions of the flower-head) (Tutin 1980).
The international expert on aquatic plants, Prof C.D.K. Cook (1990, 1998) regards C. virosa as a true aquatic species on the basis of its life history, but Preston & Croft (1997) take a narrower definition and disregard it in their British Isles treatment of aquatic plants.
Despite its large, robust appearance, C. virosa is very particular in its habitat requirement, being tied to wet ground sites with permanently available water, usually shallow and either still or slow-flowing. Typical habitats include lake margins, ponds, the banks of rivers, streams and ditches, marshes, wet-meadows, tall-herb fens and, occasionally, in slightly brackish water and along salt marshes in parts of its wider range (M.F. Watson, in: Preston et al. 2002; Jonsell & Karlsson 2010).
The species is extremely sensitive to drainage operations and the major and rapid decline of C. virosa noticed in other areas of B & I is undoubtedly the result of habitat loss due to widespread drainage designed to enable or expand intensive agriculture practices and other forms of development. On the other hand, unlike many aquatic species, C. virosa is tolerant of considerable tree or shrub shade in fen-carr, being capable of withstanding conditions down to almost 50% of full sun.
While it prefers moderately fertile, nutrient-rich, base-rich, silty or muddy organic substrates and alkaline or near neutral waters, C. virosa has a wide pH tolerance, is indifferent to lime and can also survive high levels of eutrophication where many submerged species have disappeared (M.E. Braithwaite, in: Stewart et al. 1994; Jonsell & Karlsson 2010). Eutrophication has developed and become very prevalent in all of the larger lakes in NI (Eutrophication in Northern Ireland's waters: proposals for a strategy to control nutrient enrichment., Anon., undated, c. 2000, quoting 1997 data).
Fermanagh occurrence
There are post-1975 records of C. virosa from 132 tetrads in Fermanagh (25%), while by comparison M.E. Braithwaite in Stewart et al. (1994, p. 115) map a total of just 107 tetrads with post-1970 records for the whole of Britain!
C. virosa is typically found in still or slow-flowing water in the shallows around lakes, ponds, rivers and ditches. In Fermanagh, it is chiefly associated with the fen-fringed shores of the larger lakes. Although it is present throughout the whole of the Lough Erne system, Cowbane is especially frequent and abundant around the sheltered, peaty, often fen-carr wooded bays of the drowned drumlin landscape of Upper Lough Erne. In this generally shallow, hard-water lake, the intricate shoreline and very large number of small to medium sized islands, which together cover approximately 40% of the total lake area, provides many suitable sites for this species (Gibson et al. 1980).
In deeper waters, C. virosa is said to grow on floating mats of vegetation, but while this may be the case, personally the current author (RSF) and RHN have never observed it happening in Fermanagh (M.E. Braithwaite, in: Stewart et al. 1994).
Overwintering mechanism and vegetative reproduction
In the autumn, several globose rootstocks form from buds near the base of the current year's rootstock as it dies and rots. These freshly formed rootstock storage organs serve as the overwintering organ of the species and they also contain air chambers. The new rootstocks generally grow just above ground level and during winter or spring flooding events they can readily detach and float downstream, spreading the plant vegetatively throughout the water catchment (Mulligan & Munro 1981; Jonsell & Karlsson 2010).
Flowering reproduction
The mature plant produces a succession of large white-flowered inflorescences, 8-15 cm wide, in July and August. The numerous flowers are tiny, 2 mm diameter, the petals with an incurved point (Butcher 1961). Nectar and plentiful pollen attracts a wide variety of unspecialised insect visitors which transfer the pollen. The flowers are also self-compatible and if not crossed will self-pollinate. The schizocarp fruit consists of two large, single-seeded mericarps joined laterally and each surrounded by a spongy fruit coat with five blunt ridges containing large air spaces that keeps them buoyant, enabling their water dispersal (Mulligan & Munro 1981; Jonsell & Karlsson 2010). The seed is transient in the soil seed bank, surviving for one year or less (Thompson et al. 1997).
Toxicity
All parts of the plant are poisonous, but the rootstock and lower stem are especially toxic. Consumption of even a portion of the latter is sufficient to kill a cow or a horse. The poison is a yellow oily juice called 'cicutoxin' which rapidly attacks the central nervous system, causing painful convulsions, nausea and death. Not surprisingly, measures are very often taken by farmers to eradicate the plant from around waters where animals drink or might feed. The toxin turns reddish-brown after exposure to the air, but it survives drying very well. Thus Cowbane roots excavated by ditch cleaning operations and left lying around on the soil surface, can still cause the death of animals long after they have been dug up. Cattle are particularly susceptible on account of their feeding habits, and hence the English common name 'Cowbane' is very apt, although a name like 'Farmer's Bane', would be even more appropriate. Cows are known to pull the highly toxic rootstocks and roots out of the soil, especially in the spring when the ground is soft (Mulligan & Munro 1981).
The leaves and stems are poisonous to a lesser extent and they are sometimes eaten by hungry stock when grass or other fodder is in short supply (Cooper & Johnson 1998). Fortunately, the strong, rather bitter, unpleasant (but to some people celery-like), smell of all its parts, is usually sufficient to deter both browsing animals and people; human poisoning as a result of misidentification is rare (Knees 1989). However, since 1900, a total of 83 cases of Cicuta poisoning in man have been reported in literature for the United States of America (Starreveld & Hope 1975). There are four Cicuta species in N America, of which only one is less than deadly poisonous to humans and stock animals (C. bulbifera L.) (Mulligan & Munro 1981).
British and Irish occurrence
C. virosa was previously quite widespread in Britain, particularly in the eastern half of the country. The distribution has become very local and fragmented, being mainly confined to meres in Shropshire (VC 40) and Cheshire (VC 58) and the Norfolk Broads. It occurs more rarely from S Scotland northwards to Easterness (VC 96) and the Outer Hebrides (VC 110) (Sinker et al. 1985; Preston et al. 2002). Cowbane is considered 'Nationally Scarce' in Britain, but the distribution is stable.
In Ireland, C. virosa is much more abundant, yet within NI it is still quite locally confined to the southern portion (ie the Lough Neagh and Lough Erne basins and connecting waterbodies). Altogether this very poisonous perennial is represented in a total of 16 Irish VCs (Cen Cat Fl Ir 2). There is a solitary outlying station in Co Clare (H9), remote from the main Irish distribution in the northern midlands.
European and world occurrence
C. virosa forms part of a circumpolar species complex that includes closely related species or subspecies including C. maculata L., C. douglasii (DC.) Coult. & Rose and C. bulbifera L. in N America (Mulligan & Munro 1981). The complex is mapped by Hultén & Fries (1986), Map 1412. C. virosa extends through mid-latitude, temperate, continental Europe and Asia, from France to Japan, mainly north of 45°N. It becomes more scattered in the western part of its European range and is virtually absent from the whole Mediterranean region (Tutin 1980; M.E. Braithwaite, in: Stewart et al. 1994; Jonsell & Karlsson 2010).
Names
The genus name 'Cicuta' is the Latin name of Hemlock (Conium maculatum) which, in the opinion of the current author (RSF), is more than a little bit confusing and not at all helpful (Gilbert-Carter 1964; Gledhill 1985). The connection is very probably the exceedingly poisonous and dangerous nature of both plants. The Latin specific epithet 'virosa' means 'slimy', 'rank', 'foetid' and 'poisonous' (Gilbert-Carter 1964).
Five English common names are listed for the plant, the most frequent being 'Cowbane' (from the 18th century) and 'Water Hemlock', but other interesting ones given by Britten & Holland (1886) are 'Deathin', 'Brook-tongue' and 'Scoots'. 'Deathin', a name of Scottish origin, is described as being, "peculiarly obnoxious to cows". 'Scoots' is a name associated with this and any other umbellifers frequenting wet places (Britten & Holland 1886, p. 419).
Threats
Drainage is the main threat to this erect, emergent (or rarely floating) aquatic species, since generally it is strongly tied to permanently shallow water. Provided the root of the plant is kept permanently damp, the soil surface may dry out temporarily.