Poison Hemlock: How to Identify and Potential Look-alikes

When out foraging for edible and medicinal plants, it is just as important—if not more so—to know how to identify the poisonous plants that grow in your region. Poison hemlock (Conium maculatum) is one of those that everyone should know how to identify, as it can be quite prolific in some areas. To the untrained eye it can sometimes be confused for some popular foraging plants such as Queen Anne’s lace, yarrow, wild fennel, and elderflower.

Before doing any foraging or wildcrafting, especially for plants that may resemble poison hemlock, it’s extremely important to get a foraging guidebook. Here are a few of my favorites:

• The Forager’s Harvest by Samuel Thayer
• Nature’s Garden by Samuel Thayer
• Identifying and Harvesting Edible and Medicinal Plants by Steve Brill

About poison hemlock

Poison hemlock (Conium maculatum) is in the Apiaceae family, which also includes carrots, parsnips, parsley, fennel, and their wild counterparts. It is an herbaceous biennial plant that can grow 5 to 10 feet (2-3 meters) tall or even taller.

It should not be confused with hemlock the coniferous tree which is completely harmless (and edible).

All parts of the plant are poisonous, including the flowers, leaves, stems, roots, and seeds. It contains potent toxic alkaloids that affect the nervous system, and even small internal doses can cause respiratory collapse and death.

It can also cause a severe skin reaction similar to a burn when touched externally. Definitely not a plant to mess around with!

Historically hemlock was used in ancient Greece to poison condemned prisoners, and it was what killed Socrates after he drank a potent hemlock infusion.

Where does poison hemlock grow?

Poison hemlock (Conium maculatum) is native to Europe and North Africa, but has widely naturalized in many other areas. It is found in almost every state in the United States, and in most Canadian provinces.

This USDA map shows generally where it is found in North America, and here is a more detailed map that shows which US counties it is found in.

I didn’t find any distribution maps for other countries, but poison hemlock does also grow in Europe, North Africa, Asia, Australia, and New Zealand.

Poison hemlock naturalizes very easily and can be found growing in disturbed areas, along roadsides and trails, and in damp areas along streams. In our region I find it alongside bike paths, near park edges and fields, and in dense colonies near the freeway.

If you happen to find poison hemlock in or near your yard it is advised to properly remove it as soon as possible, especially if there are children around.

How to identify poison hemlock

Poison hemlock really isn’t hard to identify, and there are a few key identification features to be on the lookout for.

Stems

The most important identification feature of poison hemlock are the stems and stalks. They are hairless, hollow, and almost always have distinctive purplish-red splotching or streaking on them, especially towards the base of the plant. These markings are a sure giveaway that it is poison hemlock.

Many sources say that the stems of poison hemlock don’t always have this splotching, though I have never found poison hemlock without it. Regardless, it’s always a good idea to know more than one identification feature, especially when dealing with poisonous plants.

Flowers

Poison hemlock flowers can be confusing because they resemble other white umbel shaped flowers, especially those in the Apiaceae family.

The flowers bloom in late spring and grow in rounded clusters that are called compound umbels. Each individual tiny flower has five petals.

After the flowers bloom they form small green fruits with wavy ribs that contain highly poisonous seeds that resemble anise, fennel, or caraway seeds.

The flowers grow on highly branched stalks that can grow up to 8-10 feet (3 meters) tall.

Leaves

The leaves of poison hemlock look very similar to parsley, chervil, and wild carrot (Queen Anne’s lace), which makes them difficult to distinguish. They are opposite and compound, hairless, lacy, and triangular in shape.

When crushed or brushed against, the leaves emit a very unpleasant musty smell, not at all carrot-like like Queen Anne’s lace.

Potential poison hemlock look-alikes

The reason it’s so important to learn how to identify poison hemlock (Conium maculatum) is because it is often mistaken for other plants that are edible and medicinal, most notably Queen Anne’s lace. Here I will explain the major differences between the edible plants that poison hemlock can potentially look similar to.

Queen Anne’s lace (Daucus carota)

There are several differences here to consider. First is overall size, as Queen Anne’s lace only grows to about 2-3 feet in size. Queen Anne’s lace has hairy stems and leaves, while poison hemlock’s are smooth. Here is one easy way to remember it: “the Queen has hairy legs.” Queen Anne’s lace flowers bloom later in the summer and have a flatter shape. They typically have a single dark purple or red flower in the center. Queen Anne’s lace also has 3 pronged bracts at the base of the flowers, and the older flowers curl up into a bird’s nest shape.

Yarrow (Achillea millefolium)

The biggest difference that yarrow has from poison hemlock is its distinctive frilly, feather-like leaves. You can see pictures of the leaves in my post about foraging yarrow. The flowers also look a bit different, as yarrow is not in the Apiaceae family so does not have a true umbel flower. Yarrow is also a smaller plant, growing about 2-3 feet in size.

Angelica (Angelica spp.)

Angelica has similar looking flowers to poison hemlock, although even more rounded and sometimes light green in color. The leaves of angelica are much larger and are compound with dozens of leaflets. There is also a sheathing base where the leaf meets the stem. Perhaps the most noticeable feature of angelica is its pleasantly fragrant scent. One thing to be aware of is that angelica can look very similar to water hemlock (Cicuta spp.), which is another highly poisonous species that can cause death.

Cow Parsnip (Heracleum maximum)

The flowers of cow parsnip are similar to poison hemlock, but much larger, and same goes for the leaves. It can also closely resemble water hemlock, so be absolutely certain of your identification.

Cow Parsley/Wild Chervil (Anthriscus sylvestris)

Cow parsley has pink stems that are slightly hairy and have a groove. Be aware that it can also closely resemble fool’s parsley, another poisonous plant.

Wild Parsnip (Pastinaca sativa)

Wild parsnip has yellow flowers and the stem is grooved. Be aware that while this plant has edible roots, the leaves and stems can cause burns and blisters on the skin after touching.

Water Parsnip (Sium suave and Berula spp.)

Water parsnip grows in marshes and wet areas, and the leaves are not lacy like poison hemlock. It looks very similar to water hemlock, another deadly plant, so great care should be taken to obtain positive identification before harvesting. I recommend using the book Incredible Wild Edibles by Samual Thayer for identifying this species.

Wild Fennel (Foeniculum vulgare)

Wild fennel has a similar overall structure to poison hemlock, but it has yellow flowers, frond like leaves, and smells strongly of fennel or anise (a licorice-like scent).

Elderflower (Sambucus spp.)

There is only one minor similarity that elderflowers might have to poison hemlock, and that is the white flowers. Elderflowers do not have the true umbel shape and are usually much larger. The plant itself is more of a large shrub and doesn’t really bear any resemblance to poison hemlock.

Three other similar looking poisonous plants

It’s also worth mentioning that there are three other poisonous plants that are also in the Apiaceae family that look somewhat similar to poison hemlock and the other plants I listed above.

• Water Hemlock (Cicuta spp.) – water hemlock is more deadly than poison hemlock and is almost as widespread. There are four different varieties, with spotted water hemlock (Cicuta maculata) being the most common.
• Giant Hogweed (Heracleum mantegazzianum) –  giant hogweed is literally giant, growing up to 18 feet (6 meters) in height with leaves that are 3-5 feet (1-2 meters) wide and flowers that can be 2.5 feet (almost 1 meter) in diameter. It causes horrible skin blistering, permanent scars, and blindness.
• Fool’s Parsley (Aethusa cynapium) – fool’s parsley is less poisonous than poison hemlock, but is still one that you most definitely want to avoid. It has hairless stems and long bracts that hang below the secondary flower clusters.

Apiaceae can be a tricky family to identify, especially when there are several poisonous species to worry about. Poison hemlock really isn’t hard to identify once you know what to look for.

This guide is here help you learn all of the features of poison hemlock and its look-alikes so that you can feel more confident in your foraging adventures!