To a lot of people, this is one of the more despicable plants: Giant Ragweed, Ambrosia trifida. This jumbo native member of the Sunflower Family, Asteraceae, is the most common source of hay fever, its scratchy little pollen particles tickling the sensibilities of many. An abundant species, Giant Ragweed is not normally something I would search out, but it is central to the strange story that follows.
When Dan Boone - yes, Daniel Boone - called late last week with news of a major find, I had to go. So, on Saturday I was down in Cincinnati to meet up with Dan, Brian Riley, Marjie Becus, and Stan Lockwood. And up the Great Miami we traipsed, to see the exciting and odd find that Jim Decker and Dan had made just a few days prior.
Except for some botanists in Indiana, who not long ago discovered a mega-rarity that associates with ragweed, and showed it to Dan. So, he and Jim Decker went looking in Ohio, and Voila!
You can see how this botanical oddity could easily be missed. Not only is no one looking for stuff in this habitat, but the ragweed absolutely overpowers the comparatively delicate broomrape, and renders it somewhat invisible.
River Broomrape, like the rest of the 200+ species of Orobanche, has little to no chlorophyll, and must attach to a suitable host via specialized root structures known as haustoria. It then extracts all of its essential nutrients from the host plant. The large root extending up from the bottom left of the photo belongs to the ragweed. The thick, fleshy yellow stems on the right are the subterranean portions of the broomrape.
It wasn't long before Marjie Becus spotted another broomrape, and in all we found a dozen or so new plants. I suspect that there are plenty more lurking out there. Should you find yourself of a mind, start crashing through thickets of Giant Ragweed along the banks of the Ohio River or the lowermost sections of its major tributaries. You just might unearth some more populations of this very cool plant.
Kudos to Dan and Jim for tracking down River Broomrape, without doubt one of the best botanical finds of 2010.