After I was introduced to mugwort (Artemisia vulgaris), I went looking for more mugwort plants. I found lots of them. And then I became confused because I also saw this plant and was not so sure that it was also mugwort, despite its similar leaf . . .
As it turns out, I was able to identify it as common ragweed (Ambrosia artemisiifolia). Just look at those two scientific names — Artemisia vulgaris and Ambrosia artemisiifolia. That, in itself, tells me how similar the plants are for the average person — as well as for the botanist!
Now, how can I (or you) tell these two plants apart? Let’s start with a close look at mugwort. This photo shows mugwort when it is just beginning to come up in the spring:
And a bit later in the spring . . .
You can see the leaf shape and some of the stems are a bit purple in color. Now, here is a lovely stand of mugwort during mid-spring:
Mugwort spreads easily and persists in colonies from year to year — just like common ragweed. Let’s take a closer look at the mugwort leaf . . .
. . . and the underside of the leaf:
We can see the leaf is deeply cut with what looks like tiny points or prickles at the end of each lobe. The underside of the leaf is silvery.
As the growing season progresses, mugwort extends upward — with a more narrow overall look to the plant . . .
The growing tip begins developing the inflorescence . . .
The next series of photos shows how the inflorescence develops at the tip of the mugwort plant as well as from various leaf axils.
Here’s a closer view of mugwort’s flowering spike (complete with an ant for purposes of visualizing the scale). . .
. . . and an even closer view of the mugwort flowers . . .
Let’s switch our attention back to common ragweed (Ambrosia artemisiifolia). Here it is as it begins its growth for the season . . .
Later in the early growing season . . .
In the above photo you can see some darker coloration along the top of each leaf’s petiole — similar to the more purple looking coloration of mugwort’s stems. The common ragweed has hairy stems — as does mugwort!
Let’s look more closely at the common ragweed leaf . . .
Those leaves still look just like mugwort’s leaves. Deeply cut or lobed. Tiny points on the end of the lobes. Same basic leaf shape.
As the growing season continues, common ragweed grows upward. Here it is with its developing inflorescences . . .
A closer view of the developing inflorescences . . .
Well, those look a bit different from mugwort’s developing inflorescences. Aahhh, now here is a distinguishing characteristic. Common ragweed’s flower spike looks much different from mugwort’s . . .
This close-up view of common ragweed shows both its staminate (male) flowers — at the upper right — and its pistillate (female) flowers — at the lower center:
[For more images of common ragweed — as compared to greater ragweed — check out this previous post.]
After studying all these images, how do I tell the plants apart? Especially early in the growing season before the flowers develop? Well . . . the key is to use my nose and not my eyes! Mugwort has a distinctive, strong “herbal” odor when I crush and smell its leaves. Common ragweed has very little odor to its bruised leaves. I invite you to visit these two plants and use the smell test on them.