Lemnoideae

One of the more important factors influencing the distribution of wetland plants, and aquatic plants in particular, is nutrient availability.[4] Duckweeds tend to be associated with fertile, even eutrophic conditions. They can be spread by waterfowl and small mammals, transported inadvertently on their feet and bodies,[5] as well as by moving water. In water bodies with constant currents or overflow, the plants are carried down the water channels and do not proliferate greatly. In some locations, a cyclical pattern driven by weather patterns exists in which the plants proliferate greatly during low water-flow periods, then are carried away as rainy periods ensue.

Duckweed is an important high-protein food source for waterfowl. The tiny plants provide cover for fry of many aquatic species. The plants are used as shelter by pond-water species such as bullfrogs and fish such as bluegills. They also provide shade and, although frequently confused with them, can reduce certain light-generated growths of photoautotrophic algae.

Duckweed is consumed in some parts of Southeast Asia, namely Laos, Thailand, and Myanmar.[6] In addition, it is also cultivated as a vegetable in Israel.[7] It produces more protein per square meter than soybeans, so sometimes it is cited as a significant potential food source.[8]

Some initial investigations to what extent duckweed could be introduced in European markets show little consumer objection to the idea.[9] NASA's Caves of Mars Project identified duckweed as a top candidate for growing food on Mars.[10]

Despite some of these benefits, because duckweed thrives in high-nutrient wetland environments, the plants can be seen as a nuisance species when conditions favor excessive proliferation in environments that are traditionally low in nutrients or oligotrophic.

One example of this problem occurs within the Everglades, a mostly oligotrophic environment, when excess chemicals (that include fertilizers) are carried by storm runoff, or surface runoff, into its waterways.[11]

Urban runoff and agricultural pollution then begin to introduce increased levels of nutrients into the surrounding wetlands and waterways, which can cause a disruption to native ecology. These conditions allow for the invasion of a fast growing species such as duckweed to establish themselves, spread, and displace other native species such as sawgrass, and over time, result in widespread changes to the ecology of native sawgrass and slough habitats within the Everglades.[12]

Duckweeds belong to the order Alismatales and the family Araceae. (a) is a phylogenetic tree based on ribulose-1, 5-bisphosphate carboxylase large-subunit genes. (b) is a schematic ventral view of Spirodela, to show the clonal, vegetative propagation of duckweeds. Daughter fronds (F1) originate from the vegetative node (No), from the mother frond F0 and remain attached to it by the stipule (Sti), which eventually breaks off, thereby releasing a new plant cluster. Daughter fronds may already initiate new fronds (F2) themselves before full maturity. Roots are attached at the prophyllum (P). (c) shows the progressive reduction from a leaf-like body with several veins and unbranched roots to a thallus-like morphology in the Lemnoideae.

The duckweeds have long been a taxonomic mystery, and usually have been considered to be their own family, the Lemnaceae. They primarily reproduce asexually. Flowers, if present at all, are small. Roots are either very much reduced, or absent entirely. They were suspected of being related to the Araceae as long ago as 1876, but until the advent of molecular phylogeny, testing this hypothesis was difficult.

Starting in 1995, studies began to confirm their placement in the Araceae and since then, most systematists consider them to be part of that family.[13]

Their position within their family has been slightly less clear; however, several twenty-first century studies place them in the position shown below.[13] Although they are in the same family as Pistia, another aquatic plant, they are not closely related.[13]

The genera of duckweeds are: Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia.

Duckweed genome sizes have a ten-fold range (150~1,500 MB), potentially representing diploids to octaploids. The ancestral genus of Spirodela has the smallest genome size (150 MB, similar to Arabidopsis thaliana), while the most derived genus, Wolffia, contains plants with the largest genome size (1,500 MB).[14] DNA sequencing has shown that Wolffiella and Wolffia are more closely related than the others. Spirodela is at the basal position of the taxon, followed by Lemna, Wolffiella, and Wolffia, which is the most derived.[15]

To identify different duckweed genomes, a DNA-based molecular identification system was developed based on seven plastid-markers proposed by the Consortium for the Barcode of Life.[16] The atpF-atpH non-coding spacer was chosen as a universal DNA barcoding marker for species-level identification of duckweeds.[17]

Extinct free-floating aquatic plants and pollen with affinities to the Lemnoideae first appear in the fossil record during the Late Cretaceous (Maastrichtian) as evidenced by floating leaves described as Aquaephyllum auriculatum from Patagonia, Argentina, and the lemnoid pollen genus Pandaniidites.[18]

Fossils of floating leaves with rootlets from the Paleocene of southern Saskatchewan, Canada, that were originally described as Lemna (Spirodela) scutata by John William Dawson in 1885, have been redescribed as Limnobiophyllum.[19] In addition to western North America, Limnobiophyllum has been reported from the Paleocene of eastern Russia and the Miocene of the Czech Republic.[19] Unusually complete specimens from the Paleocene of Alberta, Canada, range from single leaves up to about 4 cm (1.6 in) in diameter to rosettes of up to four leaves, some of which were connected to adjacent plants by stolons, and a few of which bear remains of flowers with anthers that contain Pandaniidites pollen.[20] Occurrences of lemnoid seeds described as Lemnospermum have also been reported.[19]

Research and applications of duckweeds are promoted by two international organizations, The International Lemna Association[21] and the International Steering Committee on Duckweed Research and Applications.[22]

In July 2008, the U.S. Department of Energy (DOE) Joint Genome Institute announced that the Community Sequencing Program would fund sequencing of the genome of the giant duckweed, Spirodela polyrhiza. This was a priority project for DOE in 2009. The research was intended to facilitate new biomass and bioenergy programs.[23] The results were published in February 2014. They provide insight into how this plant is adapted to rapid growth and an aquatic lifestyle.[24]

• Azolla
• Hyperaccumulators table – 3
• Neuston
• Phytoremediation
• Smallest organisms

Wikispecies has information related to Lemnoideae.

Wikimedia Commons has media related to Lemnoideae.

• Cross, John W. "The charms of duckweed". mobot.org.
• Armstrong, Wayne (n.d.). "W.P. Armstrong's exposition on and macrophotography of the Lemnaceae and allies (duckweeds)". Wayne's Word. Natural History. San Marcos, CA: Palomar College. Retrieved 16 October 2022.
• "Lemnaceae". delta-intkey.com.

derived from

Watson, L. & Dallwitz, M.J. (3 May 2006) [1992]. The Families of Flowering Plants: Descriptions, illustrations, identification, information retrieval. Archived from the original on 3 January 2007 – via delta-intkey.com.

• "Duckweed growth inhibition test". List of Standards. lemnatec.com. Archived from the original on 27 January 2013.
• "Spirodela genomics" (research lab site). SpirodelaBase. Rutgers University.