Conium maculatum L., Hemlock
Account Summary
Introduction, archaeophyte, occasional. Eurosiberian southern-temperate, but widely naturalised.
1864; Dickie, Dr G.; Newtownbutler.
April to October.
Growth form and preferred habitats
C. maculatum is a large, bushy, glabrous, hollow stemmed biennial that grows up to c 200 cm tall and is leafy and heavily branched mainly above. It looks rather like a taller form of the much more common roadside umbellifer, Anthriscus sylvestris (Cow Parsley), but the bright green stem is almost always well covered with dark purple blotches. The plant usually gives off an unpleasant, foetid, mousy odour when bruised, crushed or broken. The leaves are up to 30 cm long, bi-pinnate and the finely divided leaflets have deeply serrated margins that give the plant a rather delicate appearance, similar to Garden Parsley (Petroselinum crispum).
The species is sometimes erroneously said to be tuberous, but it has a fleshy white or pale yellow taproot, that is usually unbranched and rather like a small, narrow Parsnip (Pastinaca sativa). The current author (RSF) has found that many Floras (and not just B & I ones), describe the species without mentioning its underground parts at all! There are no tuber(s) present (Grieve 1931; Melderis & Bangerter 1955; Sell & Murrell 2009) and their lack means the species is entirely dependent on seed for its reproduction.
C. maculatum is a pioneer coloniser of bare, recently disturbed, nutrient-rich, damp to moderately dry soils. Very suitable open conditions of this nature are regularly provided by waterway dredging operations and in these situations C. maculatum can, for a time, form large colonies (Brewis et al. 1996). Hemlock is a classic nitrophile, ie a 'nitrogen-lover', or really a 'nitrogen and phosphate demander'. It shares this characteristic with the very much more common perennial Urtica dioica (Common Nettle), with which it regularly occurs, especially on farmland. The established strategy of C. maculatum is categorised as C/CR meaning it is intermediate between a Competitor and a Competitive Ruderal species (Grime et al. 1988, 2007), reflecting the tall, vigorous nature of the plant and its ability to form large colonies in suitable open, fertile habitats.
The most typical C. maculatum habitat is among other tall weeds growing in disturbed ground along lowland roadside hedgebanks, preferably in damp, heavy, but fertile, moderately acid to neutral soil. However, it also frequents other forms of open, disturbed or waste ground, especially when these are near water channels of any sort. Although it can occasionally be found in open areas within damp woodland as, for example, locally at Ely Lodge woods and in Brookeborough Deerpark, Hemlock really does not tolerate very much shade. It really prefers sunny, warm growing conditions.
Flowering reproduction
C. maculatum flowers in June and July, the compound umbel inflorescences, terminal and axillary are 2-5 cm across and have 10-20 rays bearing numerous white flowers 2 mm in diameter. The terminal umbel consists entirely of hermaphrodite (bisexual) flowers, while the lateral ones contain a mix of male and hermaphrodite flowers (Tutin 1980). The white petals are unusual in having their tips shortly inflexed (ie bent back) (Clapham et al. 1987). As in other members of the umbellifer family, nectar and pollen are well exposed and pollination is carried out by unspecified insect visitors (Proctor & Yeo 1973; Fitter 1987), which very probably include beetles, flies and bees.
The fruit is ovoid, almost globose, about 3 mm long when ripe. It is laterally compressed and is distinguished by having five prominent wavy or crinkled longitudinal ridges (Tutin 1980). The seed (mericarp) can persist in the soil for more than five years and germination is mainly, but not exclusively, in the spring (Roberts 1979).
Species status in Britain & Ireland
Until recently, in all published Britain and Ireland Floras and botanical literature, C. maculatum was believed or assumed to be a native species throughout. In the 6th edition of his An Irish Flora, Webb (1977) suggested it might possibly be introduced in Ireland and in the 2002 New Atlas the status was revised to a probable archaeophyte, ie a pre-1500 AD introduction. The decision to change the status of the species was based on evidence assembled and carefully analysed by Preston et al. (2004).
The evidence reviewed in deciding the status of the species in B & I included the fact that ancient botanists of Classical Greece knew of the plant's narcotic poisonous nature and it was, therefore, cultivated in herb gardens for many centuries and used with care in minute doses in folk medicine as a sedative and anti-spasmodic. Hemlock has been detected in archaeological deposits from the Late Bronze age and the Roman period; documentary proof (albeit pre-dating the taxonomic treatment of plants that developed from the 16th century onwards) exists that Medieval herbalists grew the plant in England as early as the tenth century, and the earliest botanical record dates from 1548 (Salisbury 1964; Preston et al. 2004).
Toxicity
The deadly poisonous nature of Hemlock is due to the presence of a range of alkaloids including coniine that act by attacking the central nervous system, inducing paralysis, convulsions and death from respiratory paralysis. All parts of the plant contain the alkaloids, the roots at all times of year proving the least poisonous. Before flowering, the leaves contain the most alkaloids (up to 2%) but the greatest concentrations are found in the flowers and the fruit. When dried, the plant loses most of its toxicity (Grieve 1931; Cooper & Johnson 1998).
The unpleasant, nauseating, mousy smell of Hemlock appears to make it unattractive to grazing animals, warning them off. Poisoning mostly occurs in spring when grazing is in short supply and the young leaves are growing along hedgebanks where the hungry animals may be able to reach them. However, this is also the period of the year when the plant is at its least toxic. Sheep are more resistant to the toxins than cattle or horses. Poisoning has also been reported in goats, pigs, rabbits, chickens, turkeys and quails.
Fatal poisoning in humans has occurred through people mistaking the plant for Wild Carrot (Daucus carota) or Garden Parsley (Petroselenum crispum) (Cooper & Johnson 1998). Children have been poisoned by making the hollow stems into whistles and pea-shooters (Grigson 1955, 1987). The best advice with regard to umbellifers is, unless the identity is absolutely definite, AVOID EVEN HANDLING THE PLANT, let alone playing with it, putting it to the mouth, or consuming it.
Use in herbal medicine
The use of C. maculatum in orthodox medicine ceased in the 19th century due to the uncertain actions of the preparations and the danger of lethal poisoning (Grieve 1931; Cooper & Johnson 1998). The purple blotched stem is sufficiently obvious that C. maculatum can easily be identified by anyone interested in using it medicinally, but it needs to be handled with great care. Unfortunately, there are a number of other relatives with 'Hemlock' used as part of their English common name (eg Oenathe crocata (Hemlock Water-dropwort)) and they are also very poisonous. Hemlock has a long history of its leaves being used as a poultice on external cancers and it was also widely used in this way to treat general sores and swellings. The hemlock poultice has also been used in Ireland for treating rheumatism, burns and perhaps wounds (Allen & Hatfield 2004).
Fermanagh occurrence

When recording in the 1947-53 period, Meikle and his co-workers considered this tall biennial a frequent species in Fermanagh. However, since very nearly half of the 40 records in the current Fermanagh Flora Database are from the pre-1953 period, RHN and the current author (RSF) believe C. maculatum has suffered a local decline since then and it is now regarded as merely occasional. As the distribution map shows, records are thinly scattered across 36 Fermanagh tetrads (6.8%) but only 22 of them contain post-1975 dates.
In Fermanagh quite of number of the sites are listed in the database as 'lakeshore'; however, in such circumstances, the plant is really associated with disturbed areas on the banks of ditches and streams feeding into these larger water bodies.
British and Irish occurrence
The New Atlas hectad map indicates that Hemlock is fairly common and widespread in much of lowland Britain, becoming less frequent and more coastal towards the N & W and in Scotland. In Ireland, it is more scattered and less frequent than in S & E England and it becomes even more scattered towards the N & W and decidedly coastal.
European and world occurrence
C. maculatum originated in the Mediterranean region and W Asia, but has certainly been introduced far beyond its natural range in N Europe and many other temperate places around the world. Despite, or on account of, its deadly poisonous properties and herbal medicinal use, Hemlock is still common throughout temperate Eurasia (except the extreme north), plus in N Africa and Macronesia. The species has been introduced into temperate regions of N & S America, S Africa, Ethiopia, S Australia and New Zealand (Clapham et al. 1987; Hultén & Fries 1986, Map 1406).
Names
The genus name 'Conium' is from the Greek 'komion' or 'kōneion', either meaning 'small cone' (Hyam & Pankhurst 1995), or just a label for both the plant and the poison (Stearn 1992). The Greek 'konos' means 'a cone', which does not appear to the current author (RSF) to have any connection with this species. Another possibility is the Greek 'konas' meaning 'to whirl about', because the plant being eaten causes vertigo and death (Grieve 1931). The Latin specific epithet 'maculatum' translates as 'spotted' or 'speckled' (Gilbert-Carter 1964).
The English common name 'Hemlock', or 'Homlocke' as Gerard (1632) has it, is said to be derived from the Anglo-Saxon 'hem', meaning 'border' or 'shore' and 'leac', meaning 'leak' or 'plant' (Grieve 1931, p. 392; Harvey 1981). Prior (1879) gives a different name origin, 'healm' meaning 'straw', and hence the term 'haulm', and 'leac', 'plant', so called from the dry hollow stalks that remain after flowering. Britten & Holland (1886) show that numerous poisonous umbellifers are called 'Hemlock', or have it as a name element. Grigson (1974) takes the view that there is no clue to the meaning of the name, which he points out is found only in English.
Grigson (1955, 1987) lists a total of 30 alternative English common names for C. maculatum, several of them with 'devil', 'bad man' of 'gypsy' word elements, indicating the dangerous nature of the plant. Even Grigson's list is not exhaustive, as other writers mention additional, obscure local names (eg Grieve 1931 and Mabey 1996). Vickery (2019) lists a total of 38 English common names but, surprisingly, there does not appear to be much folk-lore associated with the species.
Threats
None.