The most hated plant in North America

Today is a very special blog post, brought to you by one of my very best(est) friends, Tanya! Everyone say Hi to Tanya! (Hi Tanya!) Tanya gets to work outside all day every day (OK, not all day every day, but she gets to be outside A LOT with her job), and has some really awesome pictures of really unusual plants in North America. This one certainly isn't uncommon, but that doesn't make it any less special! This blog is her first (of hopefully many!) guest post for my blog, and she's writing about a plant most of us absolutely hate. And if you don't know if you hate it...do you get a runny nose and red, itchy eyes in the fall? Yes? Then you hate this plant. Trust me :)

Without further ramblings by yours truly, take it away Tanya!

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Species name: Ambrosia artemisiifolia

Common name: common ragweed, annual ragweed

Location: top image from our guest contributor; images 2, 3, and 5 from melody at Dave's Garden (available HERE); image 4 from htop at Dave's Garden (available HERE)

There may be another plant that a greater number of people despise (dandelions, maybe?), but for sheer intensity of feeling, I would argue that the most hated plant around must be Common Ragweed (Ambrosia artemisiifolia).  Every year in mid-August, many of us get that old, familiar itchy-eyes and runny-nose feeling that sends us running for filtered, air-conditioned air and antihistamines, and Common Ragweed is most likely the culprit.   

As Jen mentions in THIS POST, many people blame their fall allergies on showy flowering plants like the innocent goldenrods.  But, in order to cause your allergic reaction, you must breathe in the pollen grains, which means that the plant you’re allergic to is wind-pollinated: the plant produces lots and lots of pollen light enough to be blown around in the wind, and it’s betting that some of it will land on the female parts of another plant of the same species.  Plants that use this strategy have small, inconspicuous flowers because they don’t need to expend energy to attract pollinators like bees and butterflies to carry the pollen around for them.  Common Ragweed falls into this category: its pollen can be carried by the wind for hundreds of kilometers.  It’s hard to get away from this stuff.

Common Ragweed is native to North America (Jen says: I put "non-native" for the species status so that I could have a diagram with the "Invasive" box highlighted!) but has become an invasive species in Europe and Japan.  It is a “supertramp” species (yes, that’s a legitimate ecological term), which means that it produces lots of seed, disperses widely, and does really well in disturbed habitats. When you start looking for Common Ragweed, you’ll most likely find it in highly disturbed areas, like beside roads and in agricultural fields rather than stable forested areas, so really, it’s all our fault there’s so much of this stuff around: we’ve created lots of habitat for it!  There’s probably much more Common Ragweed around now than there was when Europeans arrived in North America.  You can burn it, pull it, mow it, or kill it with chemicals, but it will most likely come back in full force the very next year.  A good argument for increasing the amount of healthy forest and grassland habitats where Common Ragweed can’t compete, I say.

Ragweed leaves are compound and finely divided, and look a little like Wild Carrot (Daucus carota, which you can read all about in THIS POST) or Yarrow (Achillea millefolium, which you can read all about in THIS POST).  The flowers and seeds are produced in a tall spike called a raceme, and the plant grows to be about one meter in height.  This means that, in many areas, it isn’t completely covered by snow throughout the winter, and any of the seeds remaining on the plant remain accessible to animals like birds and small mammals.  The seeds have a very high oil content too, which makes them even more valuable to wildlife.  When Common Ragweed is causing you or your loved ones autumn misery, think about the mice and voles that will be depending on their stored ragweed seeds to survive until spring... and in the process, spreading them all over the place so there will be lots more for next year!

The Achilles flower: common yarrow

Species name: Achillea millefolium

Common name: Yarrow

Location: Ontario

The common yarrow plant (the real yarrow; not the plant masquerading around as a yarrow with the common name "golden yarrow") is native to the Northern Hemisphere, with most subspecies native to North America. Since I have no idea what subspecies this is, I'll just give the plant the benefit of the doubt and say it's native. Even if it wasn't truly native, it would be close enough! Most common yarrow plants have either white or pink flowers, and yellow flowers would be considered incredibly unusual (and traditionally would only be one or two flowers in a sea of either white or pink). Since we as human beings like variety in our flower gardens, we have exploited the natural mutations in the yarrow population for yellow flowers, and created varieties and cultivars with varying shades of yellow flowers. The ones found in nature, however, are always either white or pink; if you see a yellow yarrow you know it's a garden escape. This isn't necessarily a bad thing depending on the variety or cultivar; as long as there wasn't too much "modification" that was done in the breeding process, all of the genes in the native population that were for disease resistance, etc., would still be in the cultivated population. In general, the longer a plant has been in domestication the poorer the competitor it is back in its native range. If you think about the challenges domesticated corn must have in reproducing, or whether or not a Yorkie dog would survive in the wild on its own, you can see how this generally holds up with domesticated species. Due to the shape of the florets within each inflorescence, the shape of each inflorescence appears to be a 5-petaled flower. This actually isn't the case, and this plant is in the sunflower family or the Asteraceae. Each inflorescence contains 4 to 5 ray florets (the ones that look like petals), and many disc florets.

Yarrow has a long history of being used as a medicinal plant; in fact, the Latin name Achillea refers to Achilles who apparently carried it with him into battles to treat the wounds of his soldiers (where one of the common names of this plant comes from; soldier's woundwort). It has been used as a diaphoretic (a chemical or group of chemicals that cause sweating; this was a very popular treatment for various "blood disorders" in ancient times), an astringent (would be very effective against facial acne since it has a relatively concentrated amount of salicylic acid in the leaves and roots), a tonic, and a stimulant. The essential oils from the flowers were extracted using the steam distillation process and used as an anti-inflammatory agent. Depending on the expert herbalist and the disorder, it was also used to either prevent bleeding or promote it. The Navajo also used it to relieve the pain associated with toothache. These are only a few of the reported medical uses of yarrow; for a complete list you can read about it on the Wikipedia page HERE.

A word of caution if you have yarrow in your garden or come in contact with it in the wild: there are some people who experience a violent skin reaction to contact with the leaf juices from broken yarrow leaves, and sometimes with the unbroken leaves themselves. This skin rash is photosensitive so is made worse by the sun, if skin irritation wasn't enough for you. There is also the reported effect that it can cause impotence in male mice, although no evidence has shown this effect is translated in humans. It's probably better to be safe then sorry with this plant; unless you know you don't show sensitivity to the plant, it's probably best to wear gardening gloves when handling it.