Least duckweed

Lemna minuta is a minute, free-floating aquatic plant of the Araceae family (formerly placed in Lemnaceae) consisting of small, flattened, leaf-like thalli (fronds) that lack any distinction between leaf and stem. Each frond is asymmetrically obovate to elliptic, 1-3 mm long, with a single rootlet 2-3 mm long hanging into the water from the underside, three faint longitudinal nerves visible in transmitted light, and a flat or very slightly convex upper surface that is pale to medium green. Fronds reproduce vegetatively by budding from a pair of lateral pouches at the base, the daughter fronds often remaining loosely attached to form small floating groups of two to four. Flowers are exceedingly rare and consist of a single tiny pistillate flower and one or two stamens together enclosed in a minute pouch on the frond margin; the fruit is a tiny utricle containing a single ribbed seed. The plants overwinter as denser fronds (turions) that sink to the sediment in cold conditions. Native to the warmer regions of North and South America and now widely naturalised in still and slow-moving fresh waters worldwide, where it can form dense surface mats.