01 of 07
Pictures of Ragweed
My pictures of ragweed will help you identify a plant that many people speak of, even though they don't know for sure what it looks like. The reason that the weed comes up in conversation and in the news so frequently is that it is the prime source of fall allergies in North America. But why do people have so much trouble identifying a plant that has such a powerful impact on the populace?
Well, it's understandable that beginners in plant identification would have a problem identifying... this weed. Look at the picture on this page, which provides a bird's-eye view of common ragweed. It is about as nondescript a weed as you will find in the plant world. There are no colorful berries on it as there are on, for example, bittersweet nightshade. Even when in bloom, its flowers can only dream of owning the character of dandelion's flowers.
But problems with identification are not limited to novices. I once went on an August wildflower walk with a woman (let's call her Wildflower Wilma) who was about as well-versed in the flora of this particular locale as anyone could be. She rattled off plant name after plant name on this tour, with the assurance of someone who was thoroughly at home in the woods. But I must admit that I was somewhat taken aback when, toward the end of the walk, Wildflower Wilma held up a mugwort plant (Artemisia vulgaris) and confidently identified it as "ragweed."
Nobody knows everything, of course. And upon further reflection, I was able to sympathize with her, to some degree, in her misidentification: if any plant can challenge ragweed for the title of Least Distinctive Weed, it's mugwort. Perhaps it's also worth noting that the botanical name of common ragweed is Ambrosia artemisiifolia. Its specific epithet is an indication that folks have noticed a resemblance between it and some members of the genus, Artemisia (for example, Silver Mound artemisia), to which mugwort belongs.
My hope is that, after viewing my pictures of ragweed on these seven pages, you'll be able to do something that even Wildflower Wilma could not do: namely, identify, beyond all doubt, a weed that has brought misery to untold millions of allergy sufferers.Continue to 2 of 7 below.
02 of 07
A Common Ragweed Leaflet
I said earlier that the purpose of this photo gallery is to help you identify the plant, ragweed, but I must now qualify that statement a bit. For it is actually two plants whose appearance I will be illustrating in these pages: namely, Ambrosia artemisiifolia and Ambrosia trifida.
Why the need to cover both plants here? Well, together, common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida) account for most of the cases of hay fever in North America in the autumn. Given... this fact, along with their close botanical ties to each other, it makes sense to present them as a tandem. As you'll see in my photos, however, these are two very different-looking weeds.
The photo above shows a leaflet of common ragweed. I say a "leaflet" to ensure that you understand that this is not the whole leaf, just a portion of it. Multiple leaflets of this sort compose a single leaf. The leaflets are essentially miniature versions of the whole leaf. Such leaves are sometimes referred to as "twice compound" (compound leaves made up of separate leaflets that are also compound).Continue to 3 of 7 below.
03 of 07
Photo of Common Ragweed Blooms
The Ambrosia genus belongs to the aster family. Don't get your hopes up, though, upon hearing that name: common ragweed blooms, as you can see from the photo above, look nothing like those of New England aster, for example. The flowers are exceedingly inconspicuous. In fact, the casual observer may not even recognize them as flowers (they're the yellowish little bumps that you see in the picture).
To be more specific, the photo above shows you what the flower spike of the male flowers of... common ragweed looks like. Using a magnifying glass, you would be able to detect the presence of five stamens on each of these male flowers.
This weed is monoecious (see What's the Difference Between Dioecious and Monoecious?). The female flowers are even easier to overlook and can be found (if, indeed, you're determined to find them) in the upper leaf axils (i.e., the angles between the upper side of a leaf or stem and the supporting stem or branch).
The bloom is succeeded by a fruit that is technically designated an "achene." It is brownish and, like the flowers, inconspicuous.Continue to 4 of 7 below.
04 of 07
When Is Ragweed Season?
According to the University of Oklahoma, we can break down ragweed season (that is, the time period during which the weed is in bloom) geographically as follows:
- Northern U.S. and Canada: early August to early October
- Florida, other areas of the Gulf Coast, Southwest: harder to determine ("potentially flowering year-round")
- The rest of the Southern U.S.: late August to late fall
The picture here shows common ragweed in its season of bloom.
Before moving on to photos of giant ragweed,... let's consider one more identifying feature on a common ragweed plant. The initial leaves (the ones that first come out after a seed germinates) will generally have some purple speckling on them. Note, however, that other weeds can display an admixture of purple, so don't jump to any conclusions. Lamb's quarters (Chenopodium album), for example, another rather nondescript weed, is often found with some purple in its leaves.Continue to 5 of 7 below.
05 of 07
Giant Ragweed, the Monster Weed
They both have "ragweed" in their common names, they both belong to the Ambrosia genus, they're both health hazards, and they're both ugly. But for all their similarities, A. artemisiifolia and A. trifida are two very different-looking plants.
The picture above shows what giant ragweed (Ambrosia trifida) looks like. Although common ragweed isn't always a short weed (size depends on growing conditions), it can't match giant ragweed in stature. The latter can stand a... staggering 15 feet tall! To put that into perspective, there are dwarf trees that don't come close to attaining such a lofty height.
The "giant" in its name is justified. Indeed, it could just as easily be dubbed "the monster weed."
Giant ragweed is especially problematic in agricultural areas -- not because it's allergenic (although it certainly is that), but because it spreads like...well, like a weed. So it gives farmers weed-control headaches.
Could such a plague of a plant possess any qualities to recommend it (even if only to play devil's advocate)? You bet. If you look hard enough, you can usually find something good to say about even the most undesirable of plants. Some caterpillars dine on Ambrosia, for example.
Moreover, Bellarmine University lists a number of uses to which giant ragweed has been put by humans. Applications in traditional medicine include:
Continue to 6 of 7 below.
- As an astringent
- As a skin disinfectant
- As an emetic
- To reduce fever
- To treat "pneumonia, nausea, intestinal cramps, diarrhea and menstrual disorders"
- As a poultice to treat insect bites and rheumatism in the joints
- As an astringent
06 of 07
Giant Ragweed's Leaf
Giant ragweed bears a "palmate" leaf. That means its shape resembles that of the palm of a hand. I suppose that description is somewhat more apt for one of the two leaves shown in this image than for the other.
For, as you can see from the image, there are two leaf types for giant ragweed: one type has five segments (and therefore truly reminds one of a hand), the other three. Don't let this discrepancy bother you excessively in your identification efforts: the fact is, if you find a... very tall weed with leaves like either of the ones pictured above, there's a good chance you've encountered giant ragweed.
There are other types of Ambrosia besides common ragweed and giant ragweed. According to the University of Tulsa, there are 21 species in North America. Ragweeds, generally speaking, thrive in dry areas, so it is not surprising that there's even a type found widely in the deserts of the American Southwest. That would be burroweed or "bur sage" (Ambrosia dumosa). Desert plant or not, this type of ragweed is just as problematic for allergy-sufferers as are other kinds.Continue to 7 of 7 below.
07 of 07
Ragweeds in Flower: Image of the Giant Type in Bloom
As you can see if you do a comparison between this picture and that on Page 3, there is some resemblance between the blooms on a common ragweed flower spike and giant ragweed flowers. It is safe to say that neither will ever win a beauty contest.
The two ragweeds have something else in common, too: both are plants that cause rashes. So as if breathing in ragweed pollen weren't enough of a concern, you also have to worry about coming into physical contact with the plants. Brushing up against... ragweeds with your skin can give you a rash.
Do you need help identifying other weeds? Please consult the following resources: