Field Guide: Hemlock or Yarrow?

Welcome back to this follow-up post! We’re discussing how to physically identify poison hemlock, as well as how to distinguish between hemlock and yarrow, whose appearances are deceptively similar.

In my previous post, we walked through hemlock’s history. Stretching all the way back to the ancient world, hemlock was known as both a deadly poison and a useful healer. Herbalists across the centuries treated it with wary respect and cautioned their readers about the razor-thin line separating a healing dose from a lethal one.

Interesting, but…so what?

At this point, you might (understandably!) be asking: okay, it’s been a pleasant jaunt down history lane, but how does this actually impact my modern life?

Well, since 2021 seems to be doing its darndest to out-catastrophe 2020, get ready to add “poisonous plant resurgence” to your bingo card! That’s right, hemlock is reported to be popping up in greater abundance this summer in several U.S. states, increasing your chances of a close encounter.

So just stay away, right?

You may ALSO be wondering: if hemlock is so dangerous, and its poisonous effects have been so well-known for basically forever, why do people still get close enough to be harmed?

Most accidental poisonings are the result of mistaken identities. As such, hemlock is a textbook example of how vitally important it is to make sure you are 100% positive on a plant’s identification before you interact with it. Let’s talk about how to do that.

Hemlock’s Modern Threat

Hemlock is a master of disguise. It is sufficiently similar in appearance to several other harmless or even beneficial plants to be easily misidentified if a person is unaware of what to look for. Examples of lookalike plants include wild carrot (aka Queen Anne’s lace), fennel, parsley and yarrow, though all can be distinguished by a visual examination if you know what to look for.

I am by no means an expert on plant identification, but as I have previously posted about yarrow and its benefits, let’s explore some key distinctions between hemlock and yarrow in terms of their appearance. As for hemlock’s other lookalikes, please refer to a reputable guide book or other source to learn how to distinguish each. Unless you have a confirmed identity for the plant you’re looking at, stay away and do not touch!

Distinguishing between Hemlock and Yarrow

Both yarrow and hemlock have clusters of small, white flowers and fairly delicate sets of leaves. These similar features make them easy to confuse, especially if you don’t have both in front of you to compare. Fortunately, there are several physical distinctions that can help you determine whether the plant in question is friend or foe. (Use the slider bars below to view and compare photos of each characteristic!)

Flowers

Personally I find the flowers the most difficult part of these two plants to distinguish. Keener eyes than mine can probably spot lots of minute differences in the tiny white flowers themselves, but if that’s not your forte either, check for the shape of the clusters. Hemlock’s clusters form an umbel, meaning that they are all on short stalks that branch out from a common point and look somewhat like the ribs of an umbrella.

It’s also worth noting for fun that cultivated yarrow can have flowers in many different colors, ranging from soft pastel pinks to bright, vivid shades of orange, red, yellow, gold…the options are plentiful if you’re looking for an ornamental yarrow, and they make very pretty pops of color in the garden. Herbalists tend to seek white yarrow for medicinal uses, however, as it is not certain whether the colorful varieties possess the same beneficial properties.

Yarrow flowers on the left; hemlock on the right
“Poison hemlock flowers” by Wendell Smith is licensed under CC BY 2.0

Height

Yarrow is a significantly shorter plant than hemlock, tending to top out at two to three feet high. Fully-grown hemlock, on the other hand, can reach heights of five to ten feet. If the plant you’re looking at is above your head, it’s not going to be yarrow.

Leaves

Though the two plants have similar leaves, there are definite differences in their leaf structure. Yarrow’s leaves are frilly, thin, and fern-like. Hemlock’s leaves are broader across the middle, flatter, and have a similar shape to those of parsley.

Yarrow on the left, hemlock on the right. Note the distinct leaf structure.
“Poison Hemlock – Conium maculatum” by tlhowes2012 is licensed under CC BY-NC-SA 2.0

Stems

Examining the stems of the plants is probably the most surefire way to tell these two apart. Yarrow’s stems are green, slightly fuzzy and grooved. Hemlock’s stems usually (though not always, as I understand it) have telltale red or purple blotches that set them apart. To help you keep track of which is which, remember that some folks call those blotches ‘Socrates’ blood’!

Yarrow on the left, hemlock’s splotchy stem on the right.
“Poison hemlock stem” by Oregon Department of Agriculture is licensed under CC BY-NC-ND 2.0

Here’s that info again for those of you who prefer charts:

	Yarrow	Poison Hemlock
Flowers	Clusters of small, white blossoms; not truely umbel-shape	True umbel clusters of small white flowers
Leaves	Frilly, thin, delicate, fern-like	Flat, broader in center, spiky lobes, shaped like parsley
Stems	Green, slightly fuzzy	Smooth, hairless, often with purplish-red splotches
Height	Medium height, approx 2-3 feet	Taller once grown, up to 5-10 feet

Once again, the surest way to keep yourself and your family safe is to avoid touching or consuming any plant material unless you have an absolutely confirmed identity of that plant. If you plan to be out in the world where you may encounter uncultivated plants, I strongly suggest bringing along a plant identification guide. Find a book or online resource that covers the specific region you plan to be in, as there can be wildly different climates and vegetation even within the same state.

Remember: If in doubt, stay away!