The smallest flowering plants in the world all come from the Lemnaceae family, according to Iowa State University. Collectively, this group of plants is called duckweed. Duckweed plants are aquatic plants that float and live on the surface of still bodies of water. These prolific growers are so hardy that they can cover the surface of a pond or even a lake in a very short amount of time, leading many states to classify these tiny flowers as nuisance plants.
Lemna are the most common type of duckweed, according to Iowa State University. The largest of these tiny flowering plants only reach a maximum width of 4 mm and have several pairs of leaves connected at the tips, with several roots dangling into the water. These larger Lemnas are easily identified by the red dot on the leaves. The smallest Lemna plants have one pair of leaves, from which a single root dangles into the water. They do not have red spots. These tiny Lemnas average between 1 and 2 mm in diameter.
The Wolffia species of duckweed has the smallest plants. The first, W. globosa, is probably the smallest flowering plant in the world, according to Palomar College. This type of duckweed looks like seeds sprinkled onto the surface of the water. These plants have no roots and are football-shaped. The simply float on the water. W. globosa, which is an Asian species of Wolffia, has plants that average only .6 mm long and .3 mm wide. This is small enough to pass through the eye of a needle. Individual plants are barely visible to the naked eye.
W. augusta is a species of duckweed found in Australia. The plants are identical in appearance to W. globosa but are slightly larger, averaging less than 1 mm in width, according to Iowa State University. They are so small that an entire bouquet made from the flowers of W. augusta would fit on the head of a pin. The microscopic flowers each contain one stamen (male reproductive organ) and one pistil (female reproductive organ), allowing them to create seeds if fertilized. The seeds from these flowers are even tinier. Each seed is smaller than a grain of table salt.