Lemna minor aka Common Duckweed

Lemna minor, or common duckweed, is a tiny floating plant. It belongs to the arum family, Araceae. Its native range spans North and Central America. It also covers temperate and subtropical parts of the Old World. It is native to Britain and Ireland. It lives in ponds, lakes, and slow streams. Quiet, nutrient-rich water suits it well.

Each plant has a flat, bright green frond. This oval frond feels fleshy and has smooth edges. A single root hangs down into the water. Fronds measure about 0.02 feet [0.006 metres] across. Many plants join to form a dense floating mat. Sources place height between 0.02 and 0.26 feet [0.006–0.08 metres]. Garden listings give a spread of 1–3 feet [0.30–0.91 metres]. Colonies can cover far larger areas of open water. Sources describe it as perennial, though individual plants have short lives.

Flowers are tiny and seldom appear, usually in summer. They may be green or white and offer little display. Flower secretions draw flies, bees, mites, and spiders. Their visits can help move pollen between plants. The fruit is a utricle, a small bladder-like fruit. Ducks and other water birds eat the plants. Fish, tadpoles, and beavers also use them as food. The floating growth gives pond creatures cover.

Grow duckweed in standing water, in sun or partial shade. Missouri Botanical Garden also reports growth in full shade. It grows fast, with cool spring and autumn weather suiting it best. It can survive on wet mud as water levels fall. Winter buds sink, then rise when spring water warms. Garden sources list USDA hardiness zones 4–10. It suits ponds and water gardens but needs regular thinning. Scoop or net out excess growth to limit its spread. Removed plants can go on the compost heap.

Rapid spread can make duckweed a troublesome pond weed. This risk rises in places without frost. No serious insect or disease problems are reported. It can curb algae growth and take up excess nutrients. Harvesting it helps remove nitrogen and phosphorus from polluted water. People sometimes eat the leaves, though PFAF rates their food value low. Sources also record medicinal use, not proof of benefit. PFAF lists no known hazards for this species. Useful Tropical Plants gives a family-based oxalate warning, without species-specific confirmation.