Duckweed

Duckweeds are small, floating to slightly submerged species of flowering plants in the genus Lemna. The simple body is leaf-like, generally flat on top and convex below, lacks stems or leaves, is oval to tear-dropped in shape, and has one unbranched root that lacks vascular (conducting) tissue. The upper surface of the plant is covered with waxy compounds so as to shed water.

Duckweeds are abundant throughout the world in freshwater ponds, lakes, and backwaters where the water is still, with the exception of the Arctic. Plants range in size from 0.05-0.8 in (1.5-20 mm) in length. One of the most widely distributed species, Lemna minor, typically grows to a length of 0.05-0.15 in (1.5-4 mm).

Reproduction in duckweeds is almost exclusively asexual, occurring as outgrowths from one end breaks off, often resulting in the development of a dense, green mat on the surface of the water. Individual bodies are generally short-lived, five to six weeks for Lemna minor. Sexual reproduction is rare in duckweeds, and appears to occur mostly in warmer regions. Flowers are unisexual and extremely simple, consisting of only one stamen in male and one pistil in female flowers. Each flower arises from a pouch in the body and is covered by a small, highly modified leaf called a spathe.

The watermeal (Wolffia) is a close relative of duckweed, and is the smallest flowering plant. Some species of watermeal consist of only a globular, rootless body, as small as 0.02 in (0.5 mm). Duckweeds and watermeals are an important food for waterfowl, which feed on these plants on the water surface.