Thursday, September 16, 2010

LOOK FOR: Ragweed (It's Causing Your Hay Fever)

If you don't have a hard, cold place in your heart for ragweed, I can only conclude that you either a) are one of the lucky 70+ percent of the population that doesn't get hay fever, or b) don't know what's causing you to sniffle constantly from August into September. I do have hay fever, and I know one of the worst perpetrators. Permit me to tell you about it.

Ambrosia artemisiifolia | Alsemambrosia - Common ragweed
Common ragweed (Ambrosia artemisiifolia)
by AnneTanne
You've probably walked by ragweed hundreds of times without even noticing it. It's a pretty non-descript plant that sends up stalks of non-descript green flowers.* Of the 17 species of ragweed in North America, not surprisingly, the most common is common ragweed (Ambrosia artemisiifolia), which grows to about 3 feet and has almost frilly leaves with many lobes. I've also come across impressive patches of great ragweed (Ambrosia trifida), which can grow 9 feet or taller; its leaves tend to have just three to five lobes (and sometimes they're just oval).

It's the non-descript green flowers that are my nemesis: instead of developing pretty, frilly things to attract pollinators, ragweed developed the ability to produce massive amounts of airborne pollen that floats around looking for other ragweed plants to fertilize. If you look closely at the individual flowers in a stalk, they're all pointing down, so they can just drop their pollen on the breeze. A billion grains of pollen per plant, in fact.

It's the carpet bombing strategy of the plant world.

Great Ragweed
Giant ragweed (Ambrosia triloba) by 'milesizz'


These innocent grains of pollen are dependent on the wind to take them where it may. And wind goes many places. Down your street, say. And, eventually, up your nose. And then, as WebMD describes it,

Your immune system reacts to them as if they were a threat...Specialized immune cells start churning out antibodies to proteins in the pollen. The ensuing cascade of biochemical reactions floods the bloodstream with histamine, a compound that causes all-too-familiar allergy symptoms...[including] sneezing, sniffling, nasal congestion...red, puffy eyes, itchy throat, and even hives.

Pass the antihistamines, please.


Ironically enough -- did you notice this above? -- the scientific name of the ragweed genus is Ambrosia. A contributor to the Wikipedia entry on ragweed speculates that this might be for the "immortal" root of the word ambrosia. But these plants are annuals -- they live less than a year. That's why they have work so hard at reproducing. Any other guesses on what Linnaeus was thinking with that name? There's a good chance he had no idea about the link to hay fever.

Ambrosia trifida GIANT RAGWEED
Close-up of ragweed flowers by 'gmayfield'
In the wild: You'll often find ragweed in disturbed places like roadsides, abandoned fields, and stream banks, especially if there's good sun. For example, there's a lot of it growing in back of the field behind Takoma Middle School, down the street from our house.

In your yard: This is a native plant that serves as food for many insects and birds. But it's doing fine on its own in the wild, thank you very much. You really, really don't need to grow more. Please.


*Thought ragweed had yellow flowers? You're not alone, judging from my search for photos for this post. But that's goldenrod. More on that next week!



Ragweed
This picture just makes me want to sneeze.
Photo credit: 'pawpaw67'

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