Wolffia duckweed is the smallest flowering plant on Earth. Wolffia duckweed measures 1/100 of an inch (0.3 mm) across. It is about the size of a speck of cornmeal.
Wolffia duckweed is green or yellow vegetative tissue–somewhat akin to a frond or very tiny leaf. It is rootless and floats on very slow-moving freshwater, usually in wetlands, ponds, and the inlets at the edge of streams and lakes. Wolffia’s flower is produced in a depression on the top surface of the plant body. It has one stamen (a male fertilizing organ) and one pistil (a female reproduction organ).
Wolffia duckweed plants commonly float together in pairs or by the thousands to form floating mats. When Wolffia duckweeds join together to form floating mats they can be seen easily by the human eye; otherwise, they are most easily seen with a microscope. Wolffia duckweed sometimes can be seen alongside other unrelated floating plants.
Botanists have classified Wolffia duckweed as free-floating thalli. Thalli is plural for thallus. A thallus is a plant that has no leaves, roots, or stems. Other thalli are algae, fungi, some liverworts, and lichens. Thalli have no vascular tissue–that is tissue that can move water and nutrients throughout the plant. Vascular plants (most of the plants that you see around you) have tissue called xylem and phloem that carry water and minerals throughout the plant helping the plant to grow tall and wide.
The seeds produced by Wolffia duckweed flowers are borne in a tiny airbag that can float. Mature duckweed plants are only a few cells thick and also contain air pockets. This helps the plant to float on or just below the water surface. Duckweed is spread on the feet and bodies of waterbirds and small mammals as well as by moving water.
Wolffia duckweed is about 40 percent protein. It is an important source of food for many waterbirds and it provides cover for the tiny offspring of water species such as bullfrogs and fish such as bluegills. Duckweed also has historically been collected by humans and eaten as a vegetable in much of Asia. Wolffia duckweed is found on nearly every continent around the world.