Giant Ragweed; the Mystery Plant Identified

July 6, 2009

A post here last week sought the identity of a mysterious plant that was growing wild in a Wisconsin gardener’s backyard. Well the plant has been identified by several readers here and verified by a plant expert to be Giant Ragweed!

Not exactly the happy ending that I was hoping for, but at least Tamara now knows to get rid of this weed that has invaded her vegetable garden. Andrew was the first to offer up the plant’s identity and even supplied the official botanical alias; Ambrosia trifida.

The Rap Sheet on Ambrosia trifida

mystery-plant-full-bodyDar agreed with Andrew and added that this weed goes by the name of horseweed in Indiana, blooms from mid July right on through the fall, can grow to huge sizes if left unchecked, and has no common beneficial uses. Simon chimed in from the U.K. with the following: “It is a weed! There are millions of them here in England that usually camp out next to railway sidings.”

Identification was also sought from outside sources as Tamara reported in a later email to Veggie Gardening Tips:

“I contacted someone on Wisconsin Public Radio with a show called Garden Talk and he tracked down the answer.  This is rather humbling because I have been growing and nurturing giant ragweed!  They were stumped too so we shouldn’t feel so bad.”

An Expert Weighs in on Giant Ragweed

Kenneth Cameron Ph.D., Director of the Wisconsin State Herbarium was the expert who eliminated all doubt in a reply to the folks at Garden Talk public radio:

“The consensus here among a few people is that this is giant ragweed (Ambrosia trifida).  Usually, this species has leaves with just three lobes, but young plants can be more dissected.  A Google image search on “giant ragweed” will pull up some pictures that look similar.”

“Hopefully the person who sent it to you does not suffer from hay fever!!  These look like they will become large plants!!!”

Plant Mysteries Coming and Going

Don’t worry Dr. Cameron; I have a feeling that Tamara has no intentions of allowing those giant ragweed plants to grow any larger in her vegetable garden now that she knows they won’t be producing tomatoes or any other edible fruits!

Thanks for the feedback and for helping Tamara to identify her mysterious plant. Since Andrew is obviously pretty good with his wild plants I’ll let him test his insect identification skills instead by sending him a copy of the book Good Bug, Bad Bug: Who’s Who, What They Do, and How to Manage Them Organically for coming up with the correct plant ID.

wild-fruitsFinally, for those of you who just can’t get enough of a good plant mystery, here’s another for you. This time it’s an unusual tree discovered by Bea growing wild in the woods of Tennessee and loaded with small exotic looking fruits of some kind! Any guesses?

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  • Andrew

    That’s a tough one. My first thought was it might be a hawthorn, but I think it is more likely something the Ericaceae family, the group that contains blueberries.

  • Jessica

    Is it a paw paw? They use to be more common then they are now. There are some that grow on a historical farm close to my home but I dont notice the trees until the fruit is ripe in Ohio it is usually ripe in August, I have never had one but my mom told me they were similar to bananas…

  • Kenny Point

    That’s a good guess Jessica but it’s not a paw paw tree. Thanks for reminding me to post the answer; its a Buffalo Nut. It was identified for Bea by a gentleman from Virginia Tech: “You found a buffalo nut, an interesting shrub. They are parasitic on other trees. Unfortunately, we do not have this in our database but you can google Pyrularia pubera.”

    As an important side note, this is a poisonous plant!

  • David Heap

    Could be Fig, or a nut of some sort (Hazel)

  • michael

    ? how does the ragweed & giant-ragweed just pop up and there must be some kind of use for the plant & i found a ton of common-ragweed’s all alongside of my house and then found one giant-ragweed plant by the mailbox the common-ragweed plant almost looks like a tomato plant i think so.

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