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
Spotted water hemlock (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
Sweet cicely (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/Spreading hedge parsley
Japanese hedge parsley (Torilis japonica) and spreading hedge parsley (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.
- Cow parsnip (Heracleum lanatum)
- Tall meadow rue (Thalictrum dasycarpum)
- Culver's root (Veronicastrum virginicum)
- Flowering spurge (Euphorbia corollata)
- Virginia mountain mint (Pycnanthemum virginianum)
- Golden alexanders (Zizia aurea)
- Field pussytoes (Antennaria neglecta)
- Bird's-foot coreopsis (Coreopsis palmata)
- Black-eyed Susan (Rudbeckia hirta)