Canadian Horseweed Does the Twist

15 Jan

Conyza canadensis


Today’s fieldtrip aborted…due to tornado warning? Ya gotta be kiddin me! A freakin’ twister. So my afternoon turned toward a different direction…looking into the recent listing of glyphosate (RoundUp) as a probable human carcinogen.   I’m not expressing opinions here other than, “well ain’t that interesting.”  This nice friendly blog is not for un-fun head-hurting controversy, so let’s merely ask how does RoundUp interface with a twister.

It is astonishing that weeds can evolve resistance to herbicides, survival of the fittest!   A lot have turned RoundUp-resistant, with one of the most resistant of the resistant being a native weed that’s everywhere and still overlooked…Canadian Horseweed. When I say everywhere, I mean everywhere: in every vacant lot, in every Florida county, in every U.S. state (yes, Alaska and Hawaii), in every Canadian province or nearly so, and almost surely on every continent except Antarctica. Yet who’d know it on sight? It looks like “weed,” although up close the flowerheads have beauty.

conyza far

All photos today by John Bradford


RoundUp resistance has turned up in this species across the U.S. and beyond. And that reveals some weird observations and questions.   First up, if resistance is so widespread geographically, did it evolve once and spread, or did it evolve multiple times in many places?  I don’t know but will vote for “lots of times.”   Convergent evolution at work.

The plot thickens.   Anybody attuned to GMO controversies dreads genetically introduced RoundUp resistance genes spreading from crops to weeds, making Superduperweeds.   But look what happened here…the weed did not receive resistance from a GMO crop, but rather cooked it up on its own.

And then it transferred resistance to another species, not crop to weed, but weed to weed by interpollination. Conyza canadensis shared resistance by hybridizing with Conyza ramosissima. The hybrids are more RoundUp resistant than the parent.

And there’s more.   How often do non-native invasives breed with native species?   Examples are few,  but there are hints in the literature of our native C. canadensis mixing genes with C. bonariensis, an invasive species called Asthmaweed here in Florida.

conyza side

So funny how one thing leads to another with strange twists. RoundUp resistance evolving in Canadian Horseweed reveals interspecific transfer of the resistance gene (but not as feared, from a GMO crop!). Attention to this brings up another fear come true: probable genetic pollution of a native by an invasive, although in weeds where nobody would notice or care.

conyza flower

And speaking of odd twists, here’s another.   Look up any smelly plant and find the usual uses against standard human discomforts. But here’s one you don’t often encounter, and it may be handy knowledge on a chilly night. Seems Horseweed puts the friction in primitive fire starters.


Posted by on January 15, 2016 in Canadian Horseweed, Uncategorized


Tags: , ,

8 responses to “Canadian Horseweed Does the Twist

  1. Janis Riley

    January 16, 2016 at 7:51 am

    Hey. …..Always enjoy your information and wit….You make me smile while I learn Thanks.

    • George Rogers

      January 16, 2016 at 8:50 am

      Thanks so much Janis……so nice to see the sun today at long last.

  2. theshrubqueen

    January 16, 2016 at 8:33 am

    Very interesting, a new biofuel that grows everywhere? Any idea why they call it Horseweed? Horses eat it or start campfires with it?

  3. George Rogers

    January 16, 2016 at 8:48 am

    Maybe it is in every horse pasture….I’ll bet they don’t eat it. Probably won’t see it soon in any of your compositions.

  4. theshrubqueen

    January 16, 2016 at 7:22 pm

    George – do you know about the In A Vase on Monday thing? it is not just me, it is an international group of bloggers who go out and pick whatever is in the garden and make a flower arrangement.

    • George Rogers

      January 16, 2016 at 7:29 pm

      Wow—thanks for telling me. What a TERRIFIC idea…really fun. I’m going to keep my eye on it for a daily dose of floral beauty. Thanks SQ!

  5. theshrubqueen

    January 16, 2016 at 7:38 pm

    I will send you
    the link.on Monday
    What’s in the garden in New Zealand, Germany, the US and the UK and more..

    • George Rogers

      January 16, 2016 at 10:23 pm

      Much appreciated!


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