Meet the Duckweed
A variety of organisms can produce a green surface on a lake or pond this time of year.
Blue-green algae can form a scum-like presence (remember from my previous blog post that blue-green algae can come in not only blue green color but also blue, green, reddish, purple or even brown.) Long strands of filamentous green algae can produce a green surface. A variety of partially submerged aquatic plants besides the ubiquitous large floating leaves of pond and water lilies can also green up a lake surface.
I find the most fascinating organisms that can put a bright green color on a lake are a set of tiny plants called duckweed. Though tiny, they can make up in numbers for their diminutive size. Because of their size and presence at the surface, duckweed plants are readily moved about by wind and current. Expect to find them in quiet waters.
So, how tiny is tiny? That varies across the four species common in our area. The largest, star duckweed, is up to 5/8 inch long. Great duckweed is up to 3/8 inch long. Small duckweed is up to 1/4 inch long and Wolfia, water meal, is the smallest of them all. Its size is not much bigger than grains of Malt-O-Meal or Cream of Wheat. It is the smallest flowering plant in the world.
Can such tiny things really matter in a lake? You bet!
These plants are a very important food for geese and ducks and can provide up to 90% of the required nutrition for these waterfowl. Muskrats, beaver and even some fish eat duckweed. It is also reported that dense mats of duckweed can reduce mosquitoes breeding success. Fronds of star duckweed can provide habitat for aquatic invertebrates and refuge for small fish.
How can you tell these four duckweed species apart? It’s easier than you might expect.
- Great duckweed has a deep magenta color on its underside and can have up to 12 tiny roots dangling beneath the surface.
- Unlike the others, fronds of star duckweed uniquely form networks of rowboat-and-oars like structures shown here.
- Small duckweed have only a single dangling root and form colonies of leaf-like plants.
- Wolfia (water meal) is much smaller than the others. Think Malt-O-Meal granule size!
For more information on aquatic plants, I recommend:
- Through the Looking Glass: A Field Guide to Aquatic Plants, Wisconsin Lakes Partnership, University of Wisconsin, Stevens Point
- Aquatic Plants of the Upper Midwest, by Paul Skawinski