hemlock
Despite their common name, poison hemlocks are not conifer s (see hemlock). [...] Though the poison is concentrated in the seeds, the entire plant is dangerous to livestock when fresh. [...] A deadly poisonous European plant (Conium maculatum) widely naturalized in North America, having bipinnately compound leaves and compound umbels of small white flowers. [1]
By far the most familiar species is Conium maculatum (Hemlock or Poison Hemlock). [2]
A true hemlock is a tall, pyramidal tree with purplish or reddish-brown bark, slender horizontal or drooping branches, and short, blunt leaves that grow from woody cushionlike structures on the twigs. [3]
It is a herbaceous biennial plant which grows between 1.5′2.5 metres (5′8 ft) tall, with a smooth green stem, usually spotted or streaked with red or purple on the lower half of the stem. [2]
Eastern hemlock (T. canadensis) occurs in eastern Canada, the Great Lakes states, and the Appalachians. [3]
The related water hemlock (any species of Cicuta) is similar in appearance and as poisonous. [1]
) is a genus of two species of highly poisonous perennial herbaceous flowering plants in the family Apiaceae, native to Europe and the Mediterranean region as Conium maculatum, and to southern Africa as Conium chaerophylloides. [2]
Two of them, gamma-coniceine and coniine are generally the most abundant and they account for most of the plant’s acute and chronic toxicity. [...] These alkaloids are synthesized by the plant from eight acetate units from the metabolic pool, forming a polyketoacid which cyclises through an aminotransferase and forms gamma-coniceine as the parent alkaloid via reduction by a NADPH -dependent reductase. [1]
Coniine causes death by blocking the neuromuscular junction in a manner similar to curare; this results in an ascending muscular paralysis with eventual paralysis of the respiratory muscles which results in death due to lack of oxygen to the heart and brain. [...] Acute toxicity, if not lethal, may resolve in the spontaneous recovery of the affected animals provided further exposure is avoided. [...] It produces a large number of seeds that allow the plant to form thick stands in modified soils, sometimes encroaching on cultivated fields, to the extent of impeding the growth of any other vegetation inside the C. maculatum area of growth. [2]
Compare eastern hemlock, western hemlock. [4]
Sources:
[1] poison hemlock: Definition from Answers.com
[2] Conium - Wikipedia, the free encyclopedia
[3] hemlock: Definition from Answers.com
[4] Hemlock | Define Hemlock at Dictionary.com