Lemnoideae
Duckweeds are tiny, rootless or rooted floating plants with simple structure.
Duckweeds, also called water lentils or water lenses, are a subfamily of flowering aquatic plants that float on or just under the surface of still or slow-moving freshwater and wetlands. They are also known as bayroot. These plants evolved from within the arum or aroid family (Araceae), so they are usually classified as the subfamily Lemnoideae within Araceae. Older classifications, especially those from before the end of the twentieth century, treat them as a separate family called Lemnaceae.
Their structure is simple, with no obvious stem or leaves. Most of the plant is a small, organized thallus or frond just a few cells thick, often containing air pockets (aerenchyma) that help it float. Depending on the species, each plant may have no roots, or one or more simple rootlets.
Reproduction is mostly by asexual budding (vegetative reproduction) from a meristem at the base of the frond. Occasionally, three tiny “flowers” appear—two stamens and a pistil—allowing sexual reproduction. Some experts consider this “flower” a pseudanthium, or reduced inflorescence, made of three separate male or female flowers derived from the spadix in the Araceae. The evolution of the duckweed flower is still unclear because these plants are so greatly reduced compared to their relatives.
The flower of the duckweed genus *Wolffia* is the smallest known, just 0.3 mm long. The fruit produced from this occasional sexual reproduction is a utricle, and the seed develops inside a bag of air that helps it float.
In natural environments, nutrient availability is a key factor for wetland and aquatic plants. Duckweeds thrive in fertile, even eutrophic conditions. They spread by sticking to the feathers of waterfowl or the skin and fur of other amphibious animals, and are carried to new waters by flooding or moving water. In bodies of water with constant currents or overflow, they don’t proliferate much because they prefer still water. But in some places, weather patterns create a cycle: duckweeds multiply heavily during calm periods, then get washed away when rains come.
Duckweed is an important, high-protein food for waterfowl and many fish. The tiny plants also provide cover for vulnerable fry and tadpoles, and shelter for pond species like bullfrogs, newts, and bluegills.
Quick Facts
- Taxon
- Lemnoideae
Facts from the source article.
Lore & Background
Duckweeds have long been a taxonomic mystery, usually considered their own family (Lemnaceae) until molecular phylogeny confirmed their placement within Araceae starting in 1995. They primarily reproduce asexually by budding from a meristem at the base of the frond; occasionally, tiny flowers (two stamens and a pistil) are produced, with the flower of Wolffia being the smallest known at 0.3 mm. The fruit is a utricle containing a seed in an air-filled bag for flotation.
Fossil evidence places extinct duckweed-like plants in the Late Cretaceous (Maastrichtian) of Patagonia, with leaves described as Aquaephyllum auriculatum and pollen as Pandaniidites. Paleocene fossils from Canada and Russia, originally described as Lemna (Spirodela) scutata, have been redescribed as Limnobiophyllum, showing rosettes of leaves and flowers with anthers containing Pandaniidites pollen. Duckweeds are associated with fertile, eutrophic conditions and can be spread by waterfowl, amphibians, or flooding.
Reader's Guide
Duckweeds are ecologically significant as a high-protein food source for waterfowl and fish, and as shelter for fry, tadpoles, bullfrogs, newts, and bluegills. They provide shade and can reduce certain algal growths. However, in oligotrophic environments like the Everglades, excess nutrients from urban runoff or agricultural pollution can cause duckweed to proliferate excessively, displacing native species such as sawgrass and altering wetland ecology.
In human use, duckweed is consumed in Laos, Thailand, and Myanmar, produces more protein per square meter than soybeans, and is cultivated as a vegetable in Israel. NASA's Caves of Mars Project identified it as a candidate for Martian food production. Research by the U.S. Department of Energy and universities explores duckweed as a biofuel source due to its rapid growth and high starch yield, and its ability to remove carbon dioxide. Duckweeds also serve in bioremediation by absorbing excess nitrogen and phosphates.
Did You Know?
- Duckweed can double its biomass within four and a half days.
- Fossil duckweed leaves from the Late Cretaceous (Maastrichtian) have been found in Patagonia, Argentina.
- Duckweed produces five to six times as much starch as corn per unit of area.
Frequently Asked Questions
What exactly is Lemnoideae?
Lemnoideae is the subfamily that encompasses duckweeds—tiny, mostly rootless floating plants that drift on the surface of still or slow-moving freshwater. They go by several other names, including water lentils, water lenses, and bayroot.
Are duckweeds part of the arum family or their own separate family?
Modern taxonomy places them as the subfamily Lemnoideae within Araceae, reflecting their evolutionary origin from within the arum/aroid lineage. Older pre-2000s systems treated them as a standalone family called Lemnaceae, but that arrangement is now regarded as outdated.
How quickly can duckweeds take over an aquarium?
Their total biomass can double in as little as four and a half days, which is why they colonize still water so aggressively. This explosive growth rate is the primary reason aquarists find them both fascinating and notoriously hard to keep in check.
What is the smallest flowering plant in the world?
The duckweed genus Wolffia holds the record, with flowers measuring only about 0.3 millimeters in length. These plants also display striking genome-size variation, ranging from roughly 150 MB in the basal genus Spirodela up to 1,500 MB in Wolffia.
Why are duckweeds important beyond the aquarium hobby?
Per unit of growing area they can yield five to six times as much starch as corn, making them a strong candidate for biofuel and food production. Their rapid reproduction and structurally simple bodies also make them a popular model organism in plant-biology research.
More in Aquarium and Aquatic Plants, Part 2 1-24
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