Lemna, duckweed |
Layer of duckweed from Lemna minor and L. minuta
The relatively small genus, depending on the author, contains 13–30 species that are spread all over the world. The greatly reduced plants whose shoots and leaves measure only a few millimeters, are reshaped to discoid, symmetrical or asymmetrical fronds that float freely on the water surface or just below it.
The elongated, lance-shaped or egg-shaped, flat or curved fronds can occur individually or grown together. Its surface is mostly green, the lower surface may be reddish in color. Each frond has, depending on the species, 1–7 nerves that run from the node to the apex. At the bottom, at the node, grows a single root. Along the nerve can be seen small bumps in some species.
The propagation is mainly vegetatively by outgrowing of 2 daughter fronds out of lateral pockets of the mother plant. They can stay connected to the parent front or they come off.
Rarely flowers are formed which arise from the base of the pockets. The small inflorescence is surrounded by a tiny membranous spathe and consists of a naked female flower consisting of an ovary formed from single carpel, and 1–2 naked male flowers, each with one stamen. Some authors suggest no inflorescence, but a single, hermaphrodite flower with an ovary and 1–2 stamens.
After pollination by spiders and water striders, achene-like fruits are formed, that contain 1–5 longitudinally ribbed seeds.
| Floral formula: |
| ♂ * P0 A1–2 G0 ♀ * P0 A0 G1 |
Historical publicatiuons
Theophrastus (371–287 B.C.) writes, in the lake of Orchomenus (today called Kopaïs Lake), there was a lot of it on the water, what are called Lemna.
Pliny (about 23–79 AD.) mentioned in a chapter about lenses the "swamp lens", which was present in stagnant waters. It would have a cooling effect and would therefore applied against ulcers and gout.
Dioscorides (1st century AD.) wrote about the duckweed, which he calls "pool lenses", they were a lenticular moss that would be on stagnant water. He also reported a cooling effect on ulcers and inflammation. In children, they would heal intestinal perforations.
Hildegard of Bingen (1098–1179) attributed the duckweed in combination with stronger remedies a healing effect, but then they would reduce the "unnecessary fluids".
Meaning of the species names
- minor: lat. minor = small
- minuta: lat. minutus = very small
Interesting facts
The smallest species of the genus is Lemna minuta. The plant, which was originally located only in the Americas, has been introduced to Germany around 1990.
Within the genus Lemna, L. turionifera is the only species that forms turions (winter buds).