Plant Look-a-Likes: Poison Hemlock and Osha

Plant Look-a-Likes: Poison Hemlock and Osha

By Jennifer Cook, CSU Extension and USDA-NRCS

The past few years I have seen more and more Poison Hemlock (Conium maculatum) in Colorado. This plant, along with Spotted Water Hemlock (Cicuta maculata), are poisonous to livestock and humans. Osha or Porter’s Lovage (Ligusticum porter) is an edible plant, and looks very similar to poison hemlock. Both species are members of the Apiaceae (Parsley) family, but Osha is edible while the Hemlock is very poisonous.

Let’s start with Osha, sometime called wild parsnip, Porter’s Lovage or wild celery (Ligusticum porter). This tall, broadly branching perennial plant has fern like leaves that smell like spicy celery. It grows up to 3 feet tall, and is found in meadows and aspen forests of upper montane and subalpine areas, 7,000 to 10,000 feet. 

Leaves of Osha (Ligusticum porter)

Osha roots, leaves, and seeds are edible and have antibacterial and antifungal properties. It is considered a sacred plant of Native and Hispanic Americans. Those adjusting to high altitudes can chew on a leaf or drink tea made of Osha leaves.

Poison Hemlock (Conium maculatum) is a non-native biennial that grows up to 8 feet tall. Spotted Water Hemlock (Cicuta maculata) is a native that grows up to 4 feet tall. Both species have a foul, musty smell and are found in foothills to montane ecosystems (up to 9,000 feet). 

Poision hemlock (Conium maculatum)

All parts of the Hemlock plants are poisonous. Water hemlock is considered the most poisonous of plants (2-3 bites can kill humans). This plant is famous in the ancient Greek story of Socrates death, in 399 when he drank the deadly hemlock tea. Use gloves when removing these plants. 

Spotted water hemlock (Cicuta maculata) Stems may vary in color and pattern, from solid green or purple to green with purple spots or stripes

These three plants, Osha, Water Hemlock, and Poison Hemlock, look very similar, with white umbel flowers. What are some clues to distinguish them?

• The elevation at which the plant is growing could be a helpful clue, since poison hemlock is found up to around 9,000 feet and Osha is found higher in subalpine ecosystems.
• Smell the leaves. If it smells musty its poisonous, if it smells more aromatic it’s probably Osha. 
• Look at the roots. Osha roots have a brown hairy fringe around the top of the dark root. 
• Look at the stem. If it had purple spots or stripes, it is poisonous hemlock.

Be sure to identify these properly before grazing or eating.

Refer to the Poison Hemlock factsheet - https://drive.google.com/file/d/1q1zg-vdYtZfgnTKBzMM7gc_fdSva1btY/view

Water hemlock poisoning - https://csuvth.colostate.edu/poisonous_plants/Plants/Details/47

Osha - https://plants.usda.gov/core/profile?symbol=LIPO