Lemna minor
Lemna minor, the common duckweed or lesser duckweed, is a species of Lemna (duckweed) with a subcosmopolitan distribution, native throughout most of Africa, Asia, Europe and North America, occurring everywhere that freshwater ponds and slow-moving streams occur, except for arctic and subarctic climates. It is not reported as native in Australasia or South America, though is naturalised there.
It is a floating freshwater aquatic plant, with one, two or three leaves each with a single root hanging in the water; as more leaves grow, the plants divide and become separate individuals. The root is 1–2 cm long. The leaves are oval, 1–8 mm long and 0.6–5 mm broad, light green, with three (rarely five) veins, and small air spaces to assist flotation. It propagates mainly by division, and flowers are rarely produced; when produced, they are about 1 mm diameter, with a cup-shaped membranous scale containing a single ovule and two stamens. The seed is 1 mm long, ribbed with 8-15 ribs.
It grows in water with high nutrient levels and a pH of between 5 and 9, optimally between 6.5 and 7.5, and temperatures between 6 and 33 °C. Growth of colonies is rapid, and the plant frequently forms a complete carpet across still pools when conditions are suitable. In temperate regions, when temperatures drop below 6 to 7 °C it develops small, dense, starch-filled organs called 'turions', which become dormant and sink to the water bottom for winter; the following spring, these recommence growth and float back to the surface.
