Conyza canadensis
Asteraceae
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.
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.
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.
John Bradford
George Rogers
George Rogers
Dee Staley
Treasure Coast Natives 