Western Water Hemlock (Cicuta douglasii (DC.) J.M. Coult. & Ros)
Western water hemlock is a highly toxic perennial forb and is considered one of the most poisonous plants in North America. It is poisonous to all classes of livestock and humans.
This species is commonly found in wet habitats, including sloughs, wet meadows, streambanks, irrigation ditches, and other saturated soils.
Plants produce erect, solitary stems that are hollow, smooth, and branching. Stems are often swollen at the base and characteristically purple-striped or mottled. Mature plants typically grow 2 to 6 feet tall.
Leaves are alternate and compound, divided two to three times into sharply toothed leaflets. Petioles partially sheath the stem — a distinguishing characteristic of plants in the parsnip family.
Flowering occurs in summer. Flowers are small and white, arranged in flat-topped, umbrella-like clusters (compound umbels) at the ends of stems and branches.
Western water hemlock develops thickened roots that contain extremely toxic compounds. All parts of the plant are poisonous, with the roots being the most toxic.
Quick ID Guide
Life Cycle:
•Perennial
Height:
• 2–6 feet tall
Habitat:
• Sloughs
• Wet meadows
• Streambanks
• Irrigated or saturated soils
Roots:
• Thickened, highly toxic
Stems:
• Erect and solitary
• Hollow and smooth
• Purple-striped or mottled
• Swollen at base
Leaves:
• Alternate
• Compound, twice or thrice divided
• Toothed leaflets
• Petioles partially sheath stem
Flowers (Summer):
• Small and white
• Flat-topped, umbrella-like clusters (compound umbels)
Management Options
Prevention and awareness are critical due to the plant’s extreme toxicity. Identify and monitor wet areas regularly, particularly where livestock have access. Restrict livestock access to infested wet meadows, streambanks, and sloughs whenever possible.
There are currently no approved biological control agents available for western water hemlock.
Small infestations may be managed by carefully digging out the entire root system. Extreme caution should be used during removal due to the plant’s toxicity. Protective gloves and proper disposal methods are recommended. Disturbing roots can increase exposure risk, so removal should be conducted thoughtfully.
Mowing is generally not effective and may increase livestock exposure if wilted plant material remains accessible. Grazing is not recommended under any circumstances due to the high toxicity of all plant parts.
Larger infestations may be treated with appropriate herbicides labeled for aquatic or riparian use. Applications are typically most effective when made during active growth before flowering. Because this plant grows in or near water, it is essential to select products specifically approved for use in wetland or riparian environments.
Always read and follow herbicide label instructions carefully. Contact Sublette County Weed & Pest for guidance on product selection, application rates, timing, and safety precautions.
