Terrestrial invasive species


Poison hemlock (Conium maculatum)

 

Poison Hemlock FlowerPoison Hemlock leafPoison Hemlock plant

Description:

Appearance: Biennial herbaceous plant in the carrot family, 3 - 8' tall. The hairless stems are hollow, have ridges, and are marked with purple spots or mottles. Thick white tap root. Crushed roots and leaves smell like parsnip or fennel.

Leaves: Three to four times pinnately compound, broadly triangular and fern-like in appearance. The ultimate leaflets are pinnately incised. Leaf petioles clasp the stem at nodes.

Flowers: Small white flowers with 5 petals clustered in umbels of 3 – 6 inches in diameter. Typically 3-4 umbels borne at tips of branches. Blooms from May-August.

Seeds: Seeds are flat with ridges.

Species that look similar to poison hemlock include:

  • Spotted water
    hemlock

  • Queen Anne's Lace

  • Sweet cicely

  • Japanese/Spreading
     hedge parsley

Spotted water hemlock image from Minnesota wildflower

Spotted water hemlock This link leads to an external site. (Cicuta maculata), native to Minnesota. Primarily a plant of moist to wet habitats. Leaves are most frequently twice pinnate, sometimes three times, rarely four; the ultimate leaflets are sharply serrate, not lobed or incised. Spotted water hemlock is also poisonous to humans and animals.

Queen Anne's Lace

Queen Anne's Lace (Daucus carota), non-native to Minnesota. Queen Anne's Lace has bracts at the base of each umbel of white flowers and often has a purple flower in the center of the umbel. Typically each stem bears only a single umbel. Stems are frequently hairy.

Sweet Cicely flower from Minnesota wildflowers

Sweet cicely This link leads to an external site. (Osmorhiza claytonii), native to Minnesota. Smaller plants, seldom more than 2 feet high; stems usually with some pubescence. Flowers in small clusters of 4-7 flowers each.

 

Japanese hedgparsley

Japanese hedge parsley (Torilis japonica) and spreading hedge parsley This link leads to an external site. (Torilis arvensis) are both non-native to Minnesota and invasive. The hedge parsleys have sparser leaves and more branching. The small bracts at the base of the umbels are very narrow, almost threadlike; those of poison hemlock are broader, more leaflike.


Ecological Threat:

  • **Highly poisonous** Do not ingest any parts of the plant as it is poisonous to humans and livestock. We recommend using gloves when handling the plant.

  • Can grow in dense patches and displace native species along streams, wet areas, fields, and disturbed habitats, such as roadsides.
  • Spreads by seed and is present in most states in the continental U.S.
  • Poison hemlock is native to Europe, northern Africa, and western Asia. It was introduced to North America in the 1800s as a garden plant.

Control Methods:

Mechanical

  • Hand pull while wearing gloves. Use a shovel to cut the taproot 1-2 inches below ground, then remove plant.
  • Mow plants after flowers emerge, but before seeds are formed. Repeatedly mow in future years. First year plants may be too low to the ground to be impacted by mowing. The purpose of mowing is to reduce seed set by removing the flowering stalks of second-year plants.

Chemical

  • Foliar spray of triclopyr, glyphosate, or 2, 4-D.

Additional control information

Native Substitutes:


Additional Resources