One that's important to know is poison hemlock, Conium maculatum . This plant was introduced to North America from Europe, and has often been mistaken for a garden ornamental. The plant is attractive, but can be lethal to people and animals. Poison hemlock is a member of the wild carrot family, and is common along roadsides, waterways, and in cultivated areas. It resembles anise or wild parsley, and is classified in the family Umbelliferae , the parsley family.
Poison hemlock contains volatile alkaloids that have been used as a poison since ancient times.
The famous incident of Socrates' death in Athens in 329 BC occurred when he was given the juice of poison hemlock to drink. Look closely at the stem of any plant you may suspect of being poison hemlock. These blotches and streaks on a green hollow hairless stem, and the mottled purple spots, are definite identifiers of the plant. The finely divided leaves, fern-like, resemble Queen Anne's lace. Flowers are lacy and white, appearing from late May to August.