Easily confused with : many umbellifers with similar foliage, but the purplish blotches on the stem is indicative and only rarely absent. The foetid/mousey smell also helps ID, but careful not to get any juices on your skin - the toxin readily passes through skin.
Similar to : Cow Parsley (Anthriscus sylvestris) and
Rough Chervil (Chaerophyllum temulum) but it is hairless and usually with many purplish blotches on the stem.
Not to be semantically confused with : Hemlock Water-Dropwort (Oenanthe crocata) [a highly-poisonous plant with similar name in a differing genus but within the same Umbellifer family Apiaceae]. Nor with Western Hemlock aka Western Hemlock-Spruce (Tsuga heterophylla), a very tall coniferous tree.
It is a biennial, producing basal leaves in its first year followed by flowers in the second. The specific epithet maculatum means blotchy or spotted, which the lower stems are: a purplish-red. It is far more common in the South of England, much less so in the North. Found by roads, on stream and river-banks, beside ditches and on other waste ground and rough grassland - on damp soil.
CONIINE-TYPE PIPERIDINE ALKALOIDS
Cicutine), the first ever alkaloid to be synthesized in the laboratory, is one of the simplest alkaloids known along with Nicotine, but unlike Nicotine, is one of the most poisonous. It is based upon a Piperidine ring which contains a heterocyclic nitrogen atom with a short propane side-chain. Coniine has similar clinical effects to nicotine, both being biphasic, with first a stimulatory action, followed by Central Nervous System depression and muscle paralysis of respiratory muscles, when death occurs quickly. A fatal dose is estimated to be about 5mg of coniine ingested orally per kilogram of body mass, or less than 0.1 gram for a typical body-weight. Coniine is present in the leaves of Hemlock (at a concentration of 2%) and in the un-ripe fruits and roots. Consuming just 6 - 8 leaves will kill. The symptoms may progress from drowsiness, paraesthesias (loss of sensation / 'pins and needles'), weakness, nausea, ataxia (un-coordination), extreme salivation, bradycardia (slow heart-beat) followed by tachycardia (fast heart-beat). Death is due to respiratory arrest, and occurs within 3 hours of a toxic dose. There exists a treatment regime for the various symptoms, but it might not lead to a successful outcome. Hemlock has at least five similar toxic alkaloids within it making estimation of toxic dose from Hemlock poisoning difficult to assess. Poisoning can also result from inhalation of coniine or from absorption by skin, as it is a small enough molecule to be both a volatile liquid and to penetrate the skin with ease.
Coniine is also found in
Fool's Parsley (Aethusa cynapium) and the non-native carnivorous plant
Yellow Pitcher Plant (Sarracenia flava) which is native in the southeastern United States. Coniine exhibits a burning sensation in the mouth and smells foetid or 'mousey', contributing to the awful smell of Hemlock. [Coniine might not be found in
Cowbane (Cicuta virosa) despite the synonym Cicutine which is (sometimes) applied to Coniine - Cowbane contains a differing highly toxic component, Cicutoxin, which is a
polyyne rather than a
piperidine - the alias Cicutin which is sometimes applied to Coniine might just might be a case resulting from mistaken identity of the two plants - for both plants are Umbellifers].
Coniine can exist in two differing stereoisomers, the D-(S) and L-(R) forms (and a racemic mixture of the two known as rac-Coniine), with one stereoisomer being slightly less toxic than the other but there is only about a 12% difference. Both stereoisometric forms are present in Hemlock. It slowly oxidises in air. Coniine has been used as a poison-arrow toxin and as a death sentence for naughty Greeks, the most famous of whom was Socrates.
The following four further poisonous alkaloids found within Hemlock are of less importance, presumably because of their lower concentration rather than because of any lesser toxicity? Your Author knows not, and has not been able to ascertain:
Hemlock is at its most toxic in the spring when the precursor molecule, γ-Coniciene (L-PropenylPiperidine) is at its highest concentration. γ-Coniciene is converted into Coniine (and subsequently other similar compounds as shown here) within the plant.
N-MethylConiine, as shown above right, is present in Hemlock but in smaller quantities than Coniine, and is similar to Coniine.
Conhydrine and PseudoConhydrine are isomers of each other, differing only in the position of the -OH group. Conhydrine has a foetid odour similar to that of Coniine.