There is another plant on the surface of ponds, creeks, and water channels on the Tualatin River Refuge this time of year: duckweed. In some areas it dominates the surface; in others it co-exists with Azolla. It is, as it’s name implies, a good food source for waterfowl. The following was taken largely from Wikipedia:
Duckweeds are flowering aquatic plants which float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. These plants are very simple, lacking an obvious stem or leaves. The greater part of each plant is a small organized “frond” structure only a few cells thick, often with air pockets that allow it to float on or just under the water surface. Reproduction is mostly by asexual budding. Occasionally three tiny “flowers” consisting of two stamens and a pistil are produced, by which sexual reproduction occurs.
Duckweed is an important high-protein food source for waterfowl and also is eaten by humans in some parts of Southeast Asia. As it contains more protein than soybeans, it is sometimes cited as a significant potential food source.
In July 2008 the U.S. Department of Energy (DOE) Joint Genome Institute announced that the Community Sequencing Program would fund sequencing of the genome of the giant duckweed, Spirodela polyrhiza. The research is intended to facilitate new biomass and bio-energy programs. Both Rutgers University and North Carolina State University have ongoing projects to determine if duckweed might be a source of cost-effective, clean,renewable energy. Duckweed is a good candidate as a biofuel because as a biomass it grows rapidly, has 5 to 6 times as much starch as corn, and does not contribute to global warming.
There are 38 species of duckweed, and one of the interesting variables of the plant is it’s range of sizes. The so-called “giant duckweed” (Spirodela) plant measures a mere 10 mm long. “Giant” is a relative term when it comes to duckweed. One species (Wolffia) is from just .6 mm to 1.2 mm! As mentioned above, these tiny plants actually bloom occasionally and have the world’s smallest flowers, and, it follows, the flowers produce the world’s smallest fruit. They are smaller than a single salt crystal. The variety of duckweed at the Tualatin River National Wildlife Refuge is the medium-sized Lemna is ~6 mm.
What duckweed lacks in size it makes up for in numbers. Given a large supply of nutrients and enough sun duckweed can completely cover canals, lakes, and slow-moving rivers. It can double its biomass and coverage in a couple of days. These “blooms” are a real demonstration of how simple plants can convert the sun’s energy into mass at an impressive rate.
Below is a NASA photo of Lake Maracaibo, a large lake in northern Venezuela taken during a duckweed bloom in 2004. Mats of duckweed many miles long wrap around the lake.