It’s not even June yet, and it’s already hot, with record highs popping up here and there in the South.
With all the coming heat recently I've begun thinking frequently about returning more often to my kayak as a source of relief. That is, I find my kayak a good way to leave the high ground and slip into a cool creek or pond, which further allows direct entry into the water.
For a botanist, such outings have a double reward, as it allows easy access to interesting aquatic plants, many of which occur in deep water, or may be otherwise difficult to get to and observe.
“Water milfoil,” Myriophyllum heterophyllum, is a true aquatic, flowering plant, one that consists of about 50 species all around the world (except Antarctica). In the Southeast, we have probably ten or so different species in its genus, some of which are introduced.
For the most part, these plants form elongated underwater stems, featuring lots of very, very finely divided leaves. The leaf divisions are usually narrow enough to appear threadlike, and the whole stem has something of a feathery look. (One introduced species, not the one in the picture, has the common name "parrot's feather.")
Leaves toward the base of the stems may be much different in size, and in number of divisions, from those closer to the tip. The tip of the stem is commonly exserted from the water's surface, and bears a number of very tiny, inconspicuous flowers. Depending on the species, these plants sometimes form massive accumulations of these feathery stems, often mixed with various kinds of algae, and other flowering plants, such as bladderworts.
In some instances, floating mats of vegetation can develop. The biology of these plants is intriguing, and it now appears that various native Southeastern species form hybrids with each other. And, some of these species are rare. The species pictured occurs in quiet water of farm ponds on the coastal plain from Virginia south to Alabama and central Florida.
Unfortunately, most of the introduced species are very undesirable in our ponds and lakes, forming mats. Such mats can be troublesome, of course: extreme growth of these plants can seriously affect recreational activities in ponds. For this reason, chemical controls are sometimes used to get rid of the plants.
Now, you might wonder how introduced aquatic pests just "show up" in a pond or waterway. In many cases, introduced aquatics are accidentally transported from pond to pond while attached to boats. There are also many instances of introduced, noxious species arriving when someone throws out the contents of an aquarium into a local wetland--GASP!
Sometimes those tropical water plants in the aquarium like it better in the pond they just got thrown into, and so they really take off. (By the way, if you are interested in using chemical controls for nuisance aquatic species, BE SURE to consult with your local extension agency or state office for aquatic weed control, and carefully follow all directions for application and cleanup. Regulations can be a good thing.)
EDITOR’S NOTE: John Nelson is the curator of the A. C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia, South Carolina. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196, or email firstname.lastname@example.org.