Less than 1/4 inch across, these flat, rounded plants are usually found attached in groups of 3-4. They occur in huge quantities and then are often referred to as “green scum.” They have long roots dangling below (B,C); their undersides are usually green as well. Shown (A) with the much smaller Watermeal (Wolffia species) and in (C) with the larger and more uncommon Greater Duckweed (Spirodela polyrrhiza). Identification: By far the most common of our duckweeds. Lesser duckweed is about half the size of Greater Duckweed (Spirodela polyrrhiza).