Spotted water hemlock (Cicuta maculata) is an herbaceous perennial plant. This plant is considered an obligate wetland plant, thus it is almost exclusively found in wetland areas.
Spotted water hemlock plants. Image by Florida Division of Plant Industry of Florida Department of Agriculture and Consumer Services via Bugwood.org
Toxicity
Spotted water hemlock is a very toxic plant to humans and livestock. If ingested, symptoms often lead to siezures and death within a few hours of ingestion. It can also be toxic when the toxin in the plant, cicutoxin, is absorbed through the skin. Spotted water hemlock is toxic in all stages of life, but it is most harmful in the spring. The lower stem and roots of the plant contain the bulk of its toxin, but there can also be dangerous concentrations of it in young leaves and seed heads.
For information on poisonous plants and human toxicity, visit the Upstate NY Poison Center or your state or region’s poison center. For livestock poison information, visit the Cornell Vet School’s resources for plants the are poisonous to livestock. Colorado State University also has a good page specifically on water hemlocks.
Spotted water hemlock leaves. Image by Rob Routledge of Sault College via Bugwood.org
Identification
Seedlings: Spotted hemlock cotelydons are composed of two lance-shaped leaflets and eventually grow additional young leaves that are entire with lobed margins.
Leaves: The spotted water hemlock leaves are pinnate-divided (2-3 times) with toothed leaflets. The palm-shaped leaves are alternate and grow up to 38 cm (15’)’ long and 25 cm (10’)’ wide while the lance-shaped leaflets are 2.5 to 13 cm (1-5’)’ long. The basal leaves are divided at least once into 3 or more parts.
Mature plant: Spotted water hemlock usually grows in very wet areas. Stems are erect, hairless, and typically grow 0.9-1.8 m (3-6’) tall. They are stout, branched, and characteristically pale green with purple stripes. There are a cluster of chambered taproots at the base of the plant; the base of the stem looks slightly swollen and have many narrow cross-partitions.
Spotted water hemlock leaves. Image by Steve Dewey ofUtah State University via Bugwood.org
Spotted water hemlock leaves. Photo by Laurette Ellis.
Flower/seeds:
Flowers emerge from June to August. The inflorescence is composed of many white flowers that form an umbrella shape (umbel) up to 6″ (15.2 cm) across. The individual white or greenish flowers have 5 petals, 5 long stamens and a green-white center.
Spotted water hemlock flowers. Image by Rob Routledge of Sault College via Bugwood.org
Spotted water hemlock flowerhead. Image by Steve Dewey of Utah State University via Bugwood.org
Management
Chemical control
Texas A&M University Sytem website offers suggestions for chemical and non-chemical control options. For an excellent comprehensive guideline to both chemical and non-chemical management of spotted water hemlock, please see How to Control Spotted Water Hemlock published by the Texas A&M.
Non-chemical control
Spotted water hemlock can be controlled by plowing or mowing the infested area. Repeated mowing reduces the plant’s competitiveness, lowers its energy reserves in the root, and prevents seed production. Digging up and removing taproots can control small infestations. It is important to not attempt to burn the plants as a method of disposal, as burning may release the plant’s toxins into the air.
Management of spotted water hemlock developed by the Texas A&M Agrilife Extension. https://aquaplant.tamu.edu/management-options/how-to-control-spotted-water-hemlock/
University of Florida Center for Aquatic and Invasive Plants – Spotted water hemlock. https://plants.ifas.ufl.edu/plant-directory/cicuta-maculata/
The Ohio State University’s Ohio Perennial and Biennial Weed Guide – Poison hemlock. https://www.oardc.ohio-state.edu/weedguide/single_weed.php?id=114
North Carolina Cooperative Extension formed between N.C. A&T State University and NC State University – Cicuta maculata. https://plants.ces.ncsu.edu/plants/cicuta-maculata/
USDA’s Field Guide for Managing Poison Hemlock in the Southwest. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5410121.pdf
Environment and Natural Resources Trust Fund contributed by Minnesota Environment and Natural Resources Trust – Cicuta maculata. https://www.minnesotawildflowers.info/flower/water-hemlock
Identification description for water hemlock. https://www.illinoiswildflowers.info/wetland/plants/water_hemlock.htm