The Life Cycle of Duckweed
Duckweed is a group of small, floating plants with a leaf like body that's flat on the top and slightly rounded on the bottom. Duckweed has no leaves or stems, and has a single unbranched root. It's a very primitive plant, and is found all over the world in still bodies of fresh water. Duckweed has a fairly simple life cycle that enables it to spread quickly.
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Size
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Duckweeds range in size from 1.5 to 20 mm. Lemna minor, one of the most widely found species of duckweed, is about 1.5 to 4 mm long. It can be hard to determine the point in the life cycle of a specific duckweed specimen. Botanists primarily use the length of the root to decide the age of a piece of duckweed. Longer roots belong to older plants.
Types
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Duckweed comes in many varieties. Strictly speaking, only plants belonging to the genus Lemna are duckweeds, but a number of similar plants often end up lumped under this name. Watermeal or Wolffia species are a close relative, but lack roots. They are the smallest kind of flowering plant at about 1/2 mm long. Landoltia and Spirodela species are also similar to duckweed, but have two or more roots.
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Cloning
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Duckweed is very short lived. Lemna minor, for instance, survives only five to six weeks. However, the plant almost always appears as a dense mat, since it reproduces primarily asexually. The mature duckweed produces a small outgrowth from a bud on one end, which then breaks off becoming a small new duckweed. The new plant produces a root and eventually is indistinguishable from the parent. Immature plants may remain attached to the parent until maturity.
Flowering
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Duckweed is also a flowering plant, though it rarely actually reproduces sexually. A mature duckweed plant has tiny, almost indistinguishable flowers on the surface. Each flower has two stamens and one stile. The plant can fertilize itself, but usually is fertilized by pollen from neighboring duckweeds, due to a delay in the development of the stigma.
Fruit
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Duckweed produces a small green fruit, usually somewhere between 1/2 and 2 millimeters in length. A few weeks after fertilization, the tiny duckweed fruit ripens and bursts open to release one to five seeds. These seeds sink to the bottom of the pond or body of water, eventually growing into new duckweed.
Turions
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Found primarily in duckweed relatives, turions are dormant vegetative buds. They are produced by only one Lemna species, and are darker green and smaller than their parent plant. These bits of vegetation are heavier than the parent plant, and sink to the bottom of the host pond, allowing the duckweed to overwinter. In spring, as the light in the pond or stream increases, the turions leave dormancy and develop into new duckweed fronds.
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References
- Photo Credit duckweed image by Oleg Tarasov from Fotolia.com
