They are typically biennial, forming basal rosettes in the first year of growth, and sprouting a rigid, hollow flower stalk in the second.

They grow well in nitrogen rich soil, and are able to tolerate high levels of heavy metals, such as arsenic, cadmium, and lead.

[5] Terminal inflorescences are made up of many small flowers, colored white, yellow, or green depending on the species.

Plants in the genus Conium have compound umbels, with multiple dome shaped clusters branching out from a central point.

Producing a large number of seeds, and growing in a variety of locations, these plants can be considered invasive in some cases.

As a flower develops into a fruit and matures, the alkaloids present transform from γ-coniceine, to coniine, and finally to N-methylconiine.

[9] 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.

They argue that the populations in southern Africa "may be the result of the chance introduction of a few individuals which represented genetically a very limited range of the total variability of the species."

[citation needed] Conium maculatum, also known as poison hemlock, was first described by Carl Linnaeus in his 1753 publication, Species Plantarum.

[3] Conium chaerophylloides was described by Danish plant collector Christian Friedrich Ecklon (1795–1868) and German botanist Karl Ludwig Philipp Zeyher.

[12] As of December 2020[update], Plants of the World Online accepts six species:[2] Conium chaerophylloides, growing two to three meters tall, can be distinguished by its unique yellow-green flowers.

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.

The fruit is usually larger than 4 mm long, with ridges of the same dark green or brown color as the rest of the ovary.

Some varieties of the southern African species express a moderate degree of blotching at the base of the stem, but most are simply green.

[14] Gottfried S. Fraenkel in 1959 called the distribution of secondary compounds within Apiaceae and other families reciprocal adaptive evolution.

[3] Seeds of the Conium plants fall close to the parent and primarily rely on abiotic and biotic vector transmissions for dispersal.

[3] As a weed, Conium plants can spread into grasslands and other areas with low vegetation and crowd out local grass species.

[3] In 2015, a novel Poison Hemlock Virus Y (PHVY) was isolated from leaf samples of C. maculatum with mild mosaic and vein yellowing symptoms, collected from fields in south-east Iran.

[23] 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.

[26] In addition, extracts of Conium plants were found to inhibit Fusarium pallidoroseum, a fungal disease causing twig blight in mulberry.

[7] Conium maculatum was introduced into North America as an ornamental plant, imported into the United States and southern Canada.

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.

[10][30] 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.

[30] Conium maculatum is especially known to be dangerous to pregnant and breast-feeding females and in children, where poisoning has occurred by consuming small amounts of C.

[7] An overdose of Conium maculatum can typically produce paralysis, with a toxic dose causing loss of speech followed by inhibited respiratory function and, later, death.

This plant species and others in the Conium genus are also toxic in larger mammals, including bovine, equestrian, and other domestic animals.

For animals who have started to show symptoms, support respiration and treatment with activated charcoal and a saline cathartic are used.

[30] The Greek philosopher Socrates famously died by goading a jury into sentencing him to death by hemlock (see Plato's Apology.