Bring your Hankies and Tissues: It’s Ragweed Season, Folks!

Hey there friends and family! The clock is ticking on the end of summer and we’re all trying to get in on these last bits of cheery, sunny weather. What’s one thing you want to do before our chillier weather rolls in?

Our Fall and Spring seasons of shift never cease to bother our seasonal allergies. Ragweed is Fall’s biggest culprit, so that’s what we’ll be on the lookout for this week! CVNP is home to two species of Ragweed: common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifada). We’ll talk about the identifying characteristics of those and we’ll also look at some of their tricky look-alikes! As always, I’ll be getting most of my information from Newcomb’s Wildflower Guide and John Hilty’s online Illinois Wildflower Guide.

Common ragweed (Ambrosia artemisiifolia): Crazily lobed leaves, green flower racemes, blooms beginning/middle Aug. through Oct.

Common ragweed can be found grassy prairies, but does well in disturbed locations, like roadsides and abandoned farm fields. This plant can grow to about 3’ tall and has green to reddish-pink stems that are hairy. Its leaves can be oppositely or alternately attached and are deeply and irregularly lobed, almost resembling a disgruntled fern leaf. Younger leaves might have hair on their underside, but mature leaves will be mostly hairless.

Pictured: common ragweed leaves and stem.
Credit: Photos courtesy of Weedalogues.com

At the end of the stems, you’ll find racemes (or spikes of uniformly attached flowers) of yellowish-green flowers. Ragweed has two types of flowers: staminate (or flowers that only have a stamen, or male part) and pistillate (flowers that only bear a pistil, or female part). The staminate flowers occur on the top of the raceme and make up most of this spike. This contributes to our allergy frustrations and explains why one ragweed plant can create around 1 BILLION pollen grains each year (yowza!). The pistillate flowers will grow either below the male ones or where leaves connect to the stem, both excellent locations for catching all that pollen to make seeds!

Left: common ragweed flower racemes. Middle: male flowers. Right: female flowers.
Credit: Andrew Butko, Sheldon Navie (for male and female flower pictures)

Honeybees will sometimes feed on the flowers, but since it’s a green flower, our typical pollinators don’t usually visit! Ragweed leaves, stems, and flowers are often eaten by beetles, aphids, flies, and more. Additionally, the seeds get eaten by our squirrels and voles, but are also an important winter food source for overwintering birds in Ohio!

Common ragweed’s look-alike: Common mugwort (Artemisia vulgaris): Lobed leaves, green flower panicles, blooms at the end of Aug./ beginning of Sept. through Oct.

With its lobed leaves and spiky flower inflorescence, it’s easy to confuse common ragweed for common mugwort (A. vulgaris). Common mugwort has a hairless and reddish pink stem that takes on a woody appearance near the base of the plant as the plant matures. At the stem tips, closer to the flower spike, however, the stem can be hairy and reddish-green. The leaves are alternately attached and deeply and irregularly lobed. Their lobing, however, has a more predictable pattern and is less disorganized than that of common ragweed. The leaves are hairless on top, but the underside is well-covered by small white hairs.

Left: mugwort leaves. Right: white hairs on underside of leaves.
Credit: John Hilty, courtesy Illinois Wildflowers (both photos)

Common mugwort flowers grow in what is called a panicle. A panicle, like a raceme, is a spike of flowers. Unlike a raceme, however, the flowers are not uniformly attached to the stem. In this way, common ragweed racemes look like elongated cones while common mugwort panicles look more relaxed and flowy.

Pictured: mugwort flower panicle
Credit: courtesy of Bally Robert Gardens

Giant ragweed (Ambrosia trifada): differs from common ragweed by size, leaf lobing, and habitat preferences

Like common ragweed, you’ll find giant ragweed in grassy areas. However, giant ragweed prefers richer and moister soils than common ragweed. Thus, you’ll find it in higher quality habitat, like prairies and on the edges of woodlands. Like common ragweed, few pollinators visit giant ragweed. However, large plots of giant ragweed will attract many insects, which in turn, attracts insect-eating birds like sparrows, the American redstart, indigo buntings, warblers, and other songbirds.

Living up to its name, giant ragweed can grow between 3-12’ tall. Its stem is green with white hairs and its leaves are large with 3-5 distinct lobes. Just like common ragweed, giant ragweed’s leaves can be alternately or oppositely attached, and its stems terminate in yellowish-green flower racemes.

Left: giant ragweed. Middle: giant ragweed flowers. Right: giant ragweed leaf.
Credit: First and last: John Hilty, courtesy Illinois WIldflowers; middle one: Swen Follak

Giant ragweed’s look-alike: American pokeweed (Phytolacca amricana): white to pinkish flower raceme, blooming July-mid-Aug.

When we mistake American pokeweed’s inflorescence for ragweed, we might groan at the thought of seasonal allergies as early as July! But fear not, there’s still a month or so to wait before ragweed season hits. By the time ragweed begins to bloom, American pokeweed is already producing its iconic purple berries on those bright pink stems. And remember, pokeweed’s flowers are either white or pink while ragweed’s are a yellowish-green! Lastly, pokeweed leaves are ovate (or egg-shaped) with smooth margins and prominent leaf veins. This is much different than ragweed’s lobed leaves.

From left to right: American pokeweed plant, American pokeweed leaves and hairless stem, American pokeweed flowers, American pokeweed berries.
Credit: John Hilty, courtesy Illinois Wildflowers (all four)

Once pokeweed berries form, however, we might confuse THOSE for elderberries or wild grapes. Yikes! As with any wild food, check your sources before chowing down!

Left: American pokeweed berries. Middle: American elderberries. Right: Summer grape (Vitis aestivalis)
Credit: courtesy Frozen Seed Capsules, courtesy Earthcare seeds store, and the OSU Perrenial and Biennial Weed Guide

Hopefully, this feature helps you see the difference between our park’s ragweeds and their common look-alikes. Have fun exploring out there and don’t forget to bring your hankies and tissues!

Posted by mklein1216 mklein1216, August 31, 2020 18:23

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