Duckweeds are the smallest of all flowering plants.
Worldwide there are some 37 species – all of them tiny floating discs commonly seen on the surface of lakes, ponds, and quiet streams.
Often duckweeds grow so profusely that they carpet the water surface. From a distance, these dense floating mats may be mistaken for algae, but duckweeds are actually close relatives of Jack-in-the-pulpit, calla lily, and skunk cabbage.
The smallest kinds of duckweed, called watermeal, are 1 mm or less in diameter — no bigger than candy sprinkles or the head of a pin. The largest species, giant duckweed, may reach lengths of 9-10 mm (less than half an inch) — still miniscule compared to a banyan fig, or a bamboo or a spreading live oak.
One well-studied species is lesser duckweed (Lemna minor), common throughout much of North America, including the Lowcountry.
An individual duckweed plant consists of a flat, oval, leaf-like body, actually an expanded stem. Some species have one or more threadlike roots dangling from the under surface. Internal air spaces help the plant stay afloat.
Duckweed produces tiny flowers, though rarely. Most of the time, it spreads by budding off new little plants from the main plant body. Some species also produce specialized buds that sink to the bottom and overwinter.
Ducks, along with other waterfowl, do eat duckweed. So do grass carp, mullet, tilapia, and other fish. Birds may even help distribute duckweeds to new locations via plants stuck to their feet and feathers.
In nutrient-rich habitats, duckweed can propagate rapidly, blanketing ponds and reservoirs and depleting the oxygen supply to the detriment of other organisms.
But too much duckweed may not always be a bad thing. The diminutive duckweed may, in fact, be the plant of the future.
Since profuse growths extract large quantities of nitrogen and phosphates from the water, duckweeds are now being used as natural water purifiers in many wastewater treatment systems.
And since duckweeds contain 20-35 percent protein per dry weight, composted duckweed mats could serve as inexpensive food for livestock, poultry, rabbits, and fish.
They’re a potential human food source, too, as long as the plants are gathered from pollutant-free waters. Duckweeds have, in fact, been a traditional part of some Southeast Asian cuisines.
Recent research even suggests that duckweeds hold promise as a biofuel—and thus a potential source of renewable clean energy.
Vicky McMillan, a retired biologist formerly at Colgate University,lives on Hilton Head Island. She can be reached at firstname.lastname@example.org.