Poison hemlock is a member of the Parsnip family. It is a biennial introduced from Europe that may grow up to 9 feet tall. This plant, with a fleshy stout taproot, forms a rosette of fern-like, pinnately divided leaves during the first year of growth. Stems of poison hemlock have purple spots at all growth stages. The white flowers are borne in umbrella shaped clusters, each supported by a stalk.
Poison hemlock tends to get started along ditches and waterways, and will occur along the borders of pastures and crop land. All plant parts are poisonous to humans and most domestic livestock. According to legend this plant furnished the "cup of death" given to the Greek philosopher Socrates. Children have been poisoned by using the hollow stem as a whistle. Adults have been poisoned by mistaking the plant for parsley. This plant is most common in Colorado from 5,000 to 9,000 feet.