Conium - WikiHQ

Conium ( or ) is a genus of flowering plants in the family Apiaceae. , Plants of the World Online accepts six species. These plants grow best in wet, poorly drained areas with nutrient rich soil. They grow well in nitrogen rich soil, and are able to tolerate high levels of heavy metals, such as arsenic, cadmium, and lead. Conium plants are diploid, with a chromosome number of 2n = 22 (haploid number 11). They grow from one to three meters tall, varying between species. They produce hermaphroditic flowers, which are typically insect pollinated or self-fertilized.

Stems

Conium plants are herbaceous, growing non-woody, hollow, and hairless stems. Generally, the stem is striated and light green; however, the coloring varies by species and variety. Some express purple blotching throughout, some have purple blotching localized near the base, and others have no markings at all.

Leaves

The alternate leaves are pinnately compound and finely divided, with the exact pinnation patterns varying between species and leaf type. For example, stem leaves of C. maculatum plants are typically 2-4 pinnate, but basal leaves are 1-3 pinnate. The leaves and petioles are light green. Similar to the stem coloring, some species and varieties express purple blotching on the leaves and petioles.

Flowers

Terminal inflorescences are made up of many small flowers, colored white, yellow, or green depending on the species. The flowers are grouped together in umbrella shaped umbels. Plants in the genus Conium have compound umbels, with multiple dome shaped clusters branching out from a central point. Flowers are around 2 mm across, and the umbrella shaped umbels range from 1–8 cm in diameter.

Seeds

Each plant typically produces between 1,700 and 39,000 seeds, and 40-85% will germinate in suitable conditions. However, seeds will remain viable for 3 to 6 years after dispersal. Producing a large number of seeds, and growing in a variety of locations, these plants can be considered invasive in some cases. Conium plants have leaves similar to parsley (Petroselinum crispum) and roots similar to parsnip (Pastinaca sativa). However, a few characteristics can be used to distinguish the poisonous Conium plants from other harmless Apiaceae plants.

Taxonomy

The genus name "Conium" references the Greek word koneios for 'spin' or 'whirl', alluding to the dizzying effects of the plant's poison after ingestion.

History

Conium was known to ancient Greeks, who used it for its narcotic properties and in capital punishment. It was the method used to execute Theramenes and the means by which Socrates took his own life.

Conium maculatum, also known as poison hemlock, was first described by Carl Linnaeus in his 1753 publication, Species Plantarum. It was the first described species within the genus. "Maculatum" means spotted, referencing the purple blotches characteristic of this species.

Both C. fontanum and C. sphaerocarpum were described by South African botanist Olive Mary Hilliard and English botanist Brian Laurence Burtt. Together, they published their classifications in the South African Journal of Botany in 1985.

Species

, Plants of the World Online accepts six species:

Conium chaerophylloides (Thunb.) Eckl. & Zeyh.
Conium divaricatum Boiss. & Orph.
Conium fontanum Hilliard & B.L.Burtt
Conium hilliburttorum Magee & V.R.Clark
Conium maculatum L.
Conium sphaerocarpum Hilliard & B.L.Burtt

Conium chaerophylloides

Conium chaerophylloides, growing two to three meters tall, can be distinguished by its unique yellow-green flowers. Groups of many of these small flowers make up obconical umbels. The outer rays (individual flowers) form an angle with the point of attachment, giving the umbel a cone-like shape, which fans out from the base of the inflorescence. They produce round, 4 mm long, dark brown or green fruit, with deep, lightly colored ridges.

Toxin development

The evolution of toxicity within Conium plants and within Apiaceae plants has several theories. Apiaceae plants contain secondary compounds which are compounds that are often limited to just a family, genus, or a species of plant that varies among those smaller groups and is unlikely to be essential to the day-to-day physiological needs of the plant. These secondary compounds are used to mediate the plants interactions with other organisms, such as the prevention of herbivory. Gottfried S. Fraenkel in 1959 called the distribution of secondary compounds within Apiaceae and other families reciprocal adaptive evolution. Ehrlich and Raven in 1964 called Fraenkel's process coevolution. They claimed that secondary compounds diversify by emerging as a novel compound that protects a plant from herbivory. Due to this protection from herbivory and mutation or recombination in an insect, the plant can become susceptible to herbivory once more if an insect evolves the means to detoxify or tolerate the toxin created by the secondary compound. With this new trait, the insect has a new adaptive zone with which it can diversify and the plant has a certain set of adapted herbivores.

Conium maculatum has been introduced to the Americas, southern Africa, China, New Zealand, and Australia. C. maculatum has been introduced to other parts of the world due to the transportation of grain. The plants spread very quickly and are very competitive with native grasses.

Conium plants use their toxicity as a way to mediate their ecological interactions with other species. One species of moth, Agonopterix alstroemeriana, infests C. maculatum.

Economic impact

Conium plants are poisonous to a variety of animals including cows, sheep, goats, swine, rabbits, elk, poultry, and humans. Some of the impacts of the consumption of these plants on animals include muscle spasms, diarrhea, depression, skeletal malformations, and death. In fact, the most important losses from Conium plants is through livestock toxicity. An estimated yearly loss of livestock to these plants in the western US was $340 million.

Although they are mostly found in non-crop fields, Conium plants compete with commercial agricultural plants, including several types of vegetables and grains. It has been found growing in corn, chickpea, vegetable, and orchard fields. Regions affected include Oceania, the Iberian peninsula, central Europe, and the United States. Economic losses of crops due to Conium invasion is not as widespread or severe as its affecting of animals farms, and there is little crop loss data available from those regions. In addition, extracts of Conium plants were found to inhibit Fusarium pallidoroseum, a fungal disease causing twig blight in mulberry. However, these findings have not yet been implemented in practice. There is little information on the plant's interactions with other drugs and on treatment doses. Plant hobbyists continue to cultivate this plant species today.

As plants of the Conium species are known to be dangerous to mammals, they are also used as natural fences between tracts of land to block predatory animals such as wolves. It is grown along streams or rivers and near fences and pastures. In most cases, poisoning occurs from a misidentification of the plant as an edible species, such as C. maculatum root with wild parsnips or its leaves with parsley. They are also known to cause birth defects in domesticated animals. Birds do not appear to be affected as severely when consuming these seeds of these plants, but they can also be poisoned in larger doses. Specifically, toxicity doses are 3.3 mg/kg for cattle, 15.5 mg/kg for horses and 44.0 mg/kg for sheep.

Treatment

Gastric lavage is performed on larger animals who have consumed Conium plants. For animals who have started to show symptoms, support respiration and treatment with activated charcoal and a saline cathartic are used. Support respiration and activated charcoal treatment is also given to human patients who have ingested Conium plants.) Conium maculatum (poison hemlock) is infamous in its use as a poison. A small overdose of extract of the plant causes paralysis with higher toxic doses causing a ceasing of respiratory function followed by death.

Cultivation

Historically, Conium species has been grown as ornamental plants. As it has attractive flowers to some plant breeders, it was introduced to the US from Europe as a garden plant.