Mystery Plant! #758
By John Nelson
If you are a cocker-spaniel, you may not want to look at this picture!
Here’s a plant with a kind of midwinter brutal beauty, the drying leaf stalks topped with a constellation of brown, spiny burs. You might have a feeling that this is a plant that wants to spread itself around, if it can. And it wants you (or your dog) to help.
This is a member of the sunflower family (and the botanists have determined that it a relative of the common ragweed). It is an herb that is widely distributed in North America, easily found throughout southern Canada, and in every one of our united States. It is an extremely successful weed, usually found on disturbed ground, agricultural fields, cattle lots, roadsides, and places that are being excavated. The plants get to be 2-3 feet tall, with lots of attractive, dark green leaves. Blooming takes place during the summer, and each plant produces a number of small, drab flowers. Male and female flowers will be produced on the same individual plant. (Such a plant is termed “monoecious,” and another good example of such a plant would be corn.) But it is what those female flowers develop into that has really made a name for this species.
Each flower has a tiny inferior ovary (same goes for everything else in the sunflower family, by the way). As the ovaries grow, following pollination, they are ultimately covered up by a special “involucre”–a sort of wrapping–that itself is abundantly equipped with pointed, soft spines. LOTS of them. As the season wears on, the involucre’s spines harden, becoming quite stiff, thus forming the recognizable burs. Of course, the burs will detach themselves quickly just as soon as some unfortunate critter runs through them, instantly attaching themselves. Same thing will happen with obliging socks and trouser legs, so you need to be careful around this stuff.
Clearly, the spiny burs make an effective means for this plant to get its seeds into new areas, in this case with the help of an animal. If you have ever tried to comb these things out of Fluffy’s fur, you will know what I am talking about. A bur, once attached, is only going to get more deeply embedded in fur, often needing to be cut out (carefully) from a tender ear with a pair of scissors. I have an idea that the burs sometimes are attached so deeply that they will never fall out on their own…and following the demise of whatever animal might be carrying them along, would still be associated with the carcass. In such a case, doesn’t it make sense that the seeds within the burs would benefit, upon sprouting, from an immediately available concentrated dose of fertilizer in the soil? (All that considered, you’ll want to know that the burs also float, and that this plant is commonly found in great numbers along sandbars of our larger rivers, not having anything to do with animal dispersal.)
By the way, those of you who are familiar with the paintings of John James Audubon will know his depiction of the now-extinct Carolina parakeet, a flock of them noisily chattering away in a patch of our Mystery Plant…
[Answer: “Cocklebur,” Xanthium strumarium]
John Nelson is the retired curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or email email@example.com.
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