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Identifying Water Hemlock

By: Cassandra Schroeder, PAg, Range Management Extension Specialist, Kindersley

July 2021

The dry conditions have led to an increasing number of inquiries about water hemlock. Water hemlock is the most poisonous plant in Canada, however, it is often confused with the more common and non-toxic water parsnip. These plants are closely related, have a similar appearance and grow in the same type of habitat. They have clusters of small white flowers arranged like an "umbrella." Both plants are fairly large, growing up to several feet tall. Water hemlock and water parsnip both grow in moist areas near stream banks, sloughs and other wet places, they can even be found growing together in the same areas. With all these similarities it is no wonder the two plants are often confused. However, correct identification is important to informing future management and preventing toxicity.

Water Hemlock vs Water Parsnip
Plant leaves 
Water Hemlock vs Water Parsnip
Full plants

A closer look at the plant leaves is the best way to tell the two species apart.

  • Water parsnip has narrow, finely-notched leaflets. Leaf veins are less defined and do not end at the notches. Leaflets are directly attached to the 'stem' (technically the rachis of the leaf). In other words, the leaves are sessile and only once divided.
  • Water hemlock has wider and more noticeably notched leaflets. The leaf veins extend all the way to the notches. Leaflets are branched, or twice divided. There are 'little stems' attaching the leaflets to the 'larger leaf stem.'
Water Hemlock vs Water Parsnip
Plant flowers
Water Hemlock vs Water Parsnip
Plant roots

Other subtler differences include the presence of small bracts below the flower cluster in water parsnip and the swollen base of water hemlock. A toxic, oily substance is produced in this part of the plant and can often be seen when water hemlock is dissected - this is the most poisonous part of the plant. The roots from a single plant is enough to kill a cow. Water hemlock is also poisonous to humans, so appropriate precautions need to be taken when handling these plants.

More information on management of water hemlock is available in Crop Production News.

Or contact the Agriculture Knowledge Centre at 1-866-457-2377 to speak with your nearest range management extension specialist.

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