The term “hemlock” often causes confusion, applying to both non-toxic trees and highly poisonous herbaceous plants. Hemlock trees (Tsuga) are distinct from the dangerous plants known as poison hemlock (Conium maculatum) and water hemlock (Cicuta maculata).
Hemlock Trees: The Conifers
Hemlock trees are evergreen conifers found in North America and East Asia. These Tsuga trees have soft, flat needles, typically 0.5 inches long, arranged in two rows with two white bands on their undersides. Their small, ovoid cones measure around 0.5 to 0.75 inches and hang from the branches.
Unlike their toxic namesakes, hemlock trees are not poisonous to humans or animals. Their foliage is safe to touch and has been used to make tea. These trees are frequently utilized in landscaping and for timber.
The True Culprit: Poison Hemlock
The plant often implicated in poisonings is Conium maculatum, known as poison hemlock. This herbaceous biennial plant grows 3 to 8 feet tall. A distinguishing feature is its hollow, hairless stem, typically mottled with purple or reddish splotches, particularly towards the base.
Its leaves are finely divided and fern-like, giving the plant a lacy appearance. Small white flowers arranged in umbrella-like clusters, called umbels, bloom from May to August. When crushed, the plant often emits a disagreeable, musty, or mouse-like odor.
Poison hemlock commonly thrives in disturbed areas such as roadsides, ditches, fields, and waste grounds. All parts contain highly toxic alkaloids, including coniine, which can severely affect the nervous and respiratory systems, potentially leading to respiratory failure. Even incidental skin contact can cause adverse reactions in sensitive individuals.
Water Hemlock: Another Dangerous Imposter
Another dangerous plant is Cicuta maculata, commonly known as water hemlock. It is one of the most poisonous plants in North America. Water hemlock typically grows in wet environments, including marshes, ditches, stream banks, and pond margins.
Its stems are hollow and often purple-striped or mottled, featuring distinctive cross-partitions at the nodes. The plant’s clustered, swollen roots are especially toxic due to cicutoxin, a potent neurotoxin. Water hemlock also produces small white flowers in umbrella-like clusters.
A key identifier for its leaves is that their veins fork at the tips, with one branch ending in the V-shaped sinus between adjacent leaflet lobes. Ingestion of even a small amount can be fatal, with symptoms like violent convulsions and respiratory failure appearing rapidly, sometimes within 15 minutes. This plant is particularly hazardous when its roots are mistaken for edible wild plants such as parsnips or artichokes.
What to Do in Case of Accidental Ingestion
If accidental ingestion of poison hemlock or water hemlock is suspected, immediate action is necessary. Contact emergency services or Poison Control without delay. Do not induce vomiting, as this can worsen the situation.
If safe, collect a plant sample for identification by medical professionals. Provide them with information including the suspected plant, approximate amount ingested, and any observed symptoms.
Initial symptoms can manifest within 15 minutes to a few hours and may include sweating, vomiting, dilated pupils, excessive salivation, muscle weakness, and tremors. These symptoms can progress to convulsions, respiratory failure, and kidney failure. There is no specific antidote for hemlock poisoning; treatment focuses on managing symptoms and providing supportive care.