The other day, someone here in town brought by a big plastic bag with all sorts of plant matter inside. The plants had all come from a small pond behind his home, here in Columbia, and this fellow wanted all the plants in the bag identified: he suspected that some of them were aquatic weeds, and potential nuisances. I'm rather pleased to say that we were able to identify everything in his plastic bag, and we were also able to tell him a bit about the life history and natural range of each of his plants. In this case, nearly all of them were introduced, weedy, aquatic plants, and this particular one...our Mystery Plant this week...was probably the worst of the lot.
It's an herb that is native to a large area of South America, particularly the Amazon basin. It was noted for its attractiveness as an aquatic plant, suitable for indoor and outdoor aquariums, in North America, and of course, therein is a problem. It was introduced intentionally into the USA, way back in the late 1800s. The problem is that it is easily capable of spreading itself into natural bodies of water. Now imagine how many times somebody has gotten rid of all the stuff in their aquarium (critters, too) by dumping the whole thing into a nearby pond or creek! By now, this plant can be found nearly worldwide as an aquatic weed.
The plants are quite attractive, I think, and I suppose they deserve their status as a popularly cultivated aquatic species. Rhizomes are produced below the water, and the growing stems will produce a succession of nodes, each with prominently whorled leaves, six or so, forming rings up and down the stem. Each leaf has many fine divisions, something like long skinny fingers, and so each individual leaf resembles a feather. The leaves below water aren't too pretty, but those that poke above it are attractive, usually an odd sort of bright ashy gray-green. Or even sort of bluish. It's interesting that the plants bloom rarely, even in their native home...and the flowers that are produced are nearly always female (pistillate). The plants are really good at reproducing asexually by fragmentation, so perhaps they don't need to rely much on forming seeds.
This species may now be found in North America on both Pacific and Atlantic coasts, as far north as the states of Washington and New York. It is surely likely to increase its range, unfortunately. The plants are most often found in quiet water of ditches and ponds, or in slowly flowing creeks. It is capable of forming dense, impenetrable growths, through which it is hard to get a boat. (They also say that it improves mosquito habitat. Don’t know if that’s true or not.)
By the way, if you are also interested in getting plants identified --weeds, houseplants, whatever--, remember that our Herbarium offers this as a free public service. You can send us living plants or photographs (via email works great). You can get in touch with us at 803-777-8196, or by email, at firstname.lastname@example.org.
[Answer: “Parrot-feather," Myriophylum aquaticum]
John Nelson is the curator of the A. C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia SC 29208. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196, or email email@example.com.