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Background The plant body in duckweed species has undergone reduction and simplification from the ancient Spirodela species towards more derived Wolffia species. Among the five duckweed genera, Wolffia members are rootless and represent the smallest and most reduced species. A better understanding of Wolffia frond architecture is necessary to fully explore duckweed evolution. Results We conducted a comprehensive study of the morphology and anatomy of Wolffia globosa, the only Wolffia species in China. We first used X-ray microtomography imaging to reveal the three-dimensional and internal structure of the W. globosa frond. This showed that new fronds rapidly budded from the hollow reproductive pocket of the mother fronds and that several generations at various developmental stages could coexist in a single W. globosa frond. Using light microscopy, we observed that the meristem area of the W. globosa frond was located at the base of the reproductive pocket and composed of undifferentiated cells that continued to produce new buds. A single epidermal layer surrounded the W. globosa frond, and the mesophyll cells varied from small and dense palisade-like parenchyma cells to large, vacuolated cells from the ventral to the dorsal part. Furthermore, W. globosa fronds contained all the same organelles as other angiosperms; the most prominent organelles were chloroplasts with abundant starch grains. Conclusions Our study revealed that the reproductive strategy of W. globosa plants enables the rapid accumulation of biomass and the wide distribution of this species in various habitats. The reduced body plan and size of Wolffia are consistent with our observation that relatively few cell types are present in these plants. We also propose that W. globosa plants are not only suitable for the study of structural reduction in higher plants, but also an ideal system to explore fundamental developmental processes of higher plants that cannot be addressed using other model plants.

In 2020, the first record of Wolffia arrhiza was made in Novosibirsk region (Western Siberia) in a floodplain lake. Wolffia arrhiza formed vast stands with an area of hundreds of square meters and with high productivity. Besides monodominant communities, it was met as a component of the cenoses of such hydrophytes as Stratiotes aloides and Hydrocharis morsus-ranae, as well as of the helophyte communities formed by Typha latifolia and Eleocharis mamillata. According to local residents, Wolffia was observed as abundant for some years; thus, most likely, the population winters safely at the latitude of Novosibirsk. The most likely source of Wolffia arrhiza appearance in the lake was an accidental introduction from an aquarium, although the possibility of this plant entering the lake in high-water years from the wastewater of the municipal settling tank of Novosibirsk sewage waters also exists.

Duckweeds represent a small, free-floating aquatic family (Lemnaceae) of the monocot order Alismatales with the fastest growth rate among flowering plants. They comprise five genera (Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia) varying in genome size and chromosome number. Spirodela polyrhiza had the first sequenced duckweed genome. Cytogenetic maps are available for both species of the genus Spirodela (S. polyrhiza and S. intermedia). However, elucidation of chromosome homeology and evolutionary chromosome rearrangements by cross-FISH using Spirodela BAC probes to species of other duckweed genera has not been successful so far. We investigated the potential of chromosome-specific oligo-FISH probes to address these topics. We designed oligo-FISH probes specific for one S. intermedia and one S. polyrhiza chromosome (Fig. 1a). Our results show that these oligo-probes cross-hybridize with the homeologous regions of the other congeneric species, but are not suitable to uncover chromosomal homeology across duckweeds genera. This is most likely due to too low sequence similarity between the investigated genera and/or too low probe density on the target genomes. Finally, we suggest genus-specific design of oligo-probes to elucidate chromosome evolution across duckweed genera.

The free-floating aquatic duckweeds consist of the five genera, Spirodela , Landoltia , Lemna , Wolffiella and Wolffia , comprising 36 species within the monocot order of Alismatales. They are strongly adaptable to various environments and are widely distributed in a variety of climates all over the world except that Wolffiella species are restricted to the Americas and Africa. Among them, Spirodela species have large a flattened frond with 5−11 rhizoids while the rootless Wolffia species form an oval-shaped frond and are the smallest flowering plants. Duckweeds seldom flower and their rapid asexual propagation allows them to accumulate biomass quickly. They usually bud new generations (daughter fronds) from their reproductive pouches at the base of the mother fronds and the frond number almost doubles within 24 h under good growth conditions yielding the fastest-growing flowering plants. They tend to be associated with nutrient-rich or eutrophic freshwater environments with slow-moving flow such as ponds, lakes, ditches, and paddy fields. While duckweeds become more reduced from Spirodela to Wolffia , their genome size varies 13-fold, ranging from 150 Mb in Spirodela polyrhiza to 1881 Mb in Wolffia arrhiza . With the development of long-read sequencing technology, the genomes of common duckweed species including S. polyrhiza , Lemna minor , Lemna gibba and Wolffia australiana have been sequenced and assembled. The underlying molecular mechanisms and regulatory networks in duckweeds under different treatments such as starvation, salt stress, heavy metal and radiation have also been revealed by transcriptome, proteome and metabolome analyses for the genera Spirodela , Landoltia , and Lemna enhancing their potential applications in the fields of phytoremediation and bioenergy. Furthermore, genetic transformation systems for some common duckweeds such as L. minor , Lemna aequinoctialis , S. polyrhiza and Wolffia globosa have been established, and especially the frond transformation systems have significantly improved transformation efficiencies (more than 90%). These characteristics have made duckweeds model systems for several decades for the study of plant physiology, biochemistry, ecotoxicology, and have contributed to knowledge of auxin biosynthesis, plant flowering and the circadian system. Duckweeds have also been widely used for the treatment of agricultural, municipal, and even industrial wastewater because they can uptake nitrogen and phosphorus as well as quickly accumulate heavy metals and organic pollutants. Besides, their accumulated biomass is rich in starch and protein and therefore can be used for feed applications and biofuels. In this review, we introduce the origin, classification and evolution of duckweeds, as well as research in morphology and anatomy, physiology, genetic transformation and omics studies. We further discuss the application of duckweeds in food, feed, bioenergy, and bioremediation. Finally, we highlight the challenges and future directions of duckweed research, providing a reference for basic biological research and resource utilization.

Wolffia is a genus of protein-rich aquatic plants. Mankai, a cultivated strain of Wolffia globosa, contains more than 40 % protein based on dry matter evaluation. Furthermore, Mankai is nutritionally excellent as a food material, and is expected to be applicable to various products as a substitute for animal protein. A battery of toxicological studies was conducted on the dried product of Mankai (Dry Mankai), with the expectation to utilize it as a raw material for food applications. Dry Mankai was not genotoxic in a bacterial reverse mutation test and in vitro micronucleus assay. In the subchronic toxicity study, rats were provided Dry Mankai in the diet at levels of 0 %, 5 %, 10 %, or 20 % (w/w), equivalent to 0, 3.18, 6.49, and 13.16 g/kg/day for males and 0, 3.58, 7.42, and 15.03 g/kg/day for females, respectively. No adverse effects that could be attributable to treatment were observed in clinical observations, body weight, food consumption, ophthalmology, hematology and blood chemistry, urinalysis, and macroscopic and microscopic findings. According to the repeated-dose study in rats, the no observed adverse effect level of Dry Mankai was 20 % (w/w) for both sexes (13.16 and 15.03 g/kg/day for males and females, respectively).

A 40 days feeding trial with Labeo rohita (rohu) fry was conducted in six outdoor cemented tanks (5m × 4m × 1 m; 6–8 cm soil base) to establish the relative impact of on‐farm grown live Wolffia globosa (a duckweed with crude protein of 28.57%) and a formulated iso‐nitrogenous feed (crude protein 28.37%) on growth performance, survival, health and overall quality of fingerlings. The experimental tanks were dried, limed at 250 kg/ha, filled with ground water and subsequently applied with cow dung (soaked overnight) and mustard oil cake at 1,000 kg/ha and 50 kg/ha respectively. The fry were stocked at 0.3 millions/ha in six prepared tanks, and fed live Wolffia (T1) and formulated feed (T2). Results of the study indicate better performance (p

The production of recombinant proteins in transgenic plants is becoming an increasingly serious alternative to classical biopharming methods as knowledge about this process grows. Wolffia arrhiza, an aquatic plant unique in its anatomy, is a promising expression system that can grow in submerged culture in bioreactors. In our study 8550 explants were subjected to Agrobacterium-mediated transformation, and 41 independent hygromycin-resistant Wolffia lines were obtained, with the transformation efficiency of 0.48%. 40 of them contained the hirudin-1 gene (codon-optimized for expression in plants) and were independent lines of nuclear-transformed Wolffia, the transgenic insertion has been confirmed by PCR and Southern blot analysis. We have analyzed the accumulation of the target protein and its expression has been proven in three transgenic lines. The maximum accumulation of recombinant hirudin was 0.02% of the total soluble protein, which corresponds to 775.5 ± 111.9 ng g(−1) of fresh weight of the plant. The results will be used in research on the development of an expression system based on Wolffia plants for the production of hirudin and other recombinant pharmaceutical proteins.

Plants in the family Lemnaceae are aquatic monocots and the smallest, simplest, and fastest growing angiosperms. Their small size, the smallest family member is 0.5 mm and the largest is 2.0 cm, as well as their diverse morphologies make these plants ideal for laboratory studies. Their rapid growth rate is partially due to the family’s neotenous lifestyle, where instead of maturing and producing flowers, the plants remain in a juvenile state and continuously bud asexually. Maturation and flowering in the wild are rare in most family members. To promote further research on these unique plants, we have optimized laboratory flowering protocols for 3 of the 5 genera: Spirodela, Lemna, and Wolffia in the Lemnaceae. Duckweeds were widely used in the past for research on flowering, hormone and amino acid biosynthesis, the photosynthetic apparatus, and phytoremediation due to their aqueous lifestyle and ease of aseptic culture. There is a recent renaissance in interest in growing these plants as non-lignified biomass sources for fuel production, and as a resource-efficient complete protein source. The genome sequences of several Lemnaceae family members have become available, providing a foundation for genetic improvement of these plants as crops. The protocols for maximizing flowering described herein are based on screens testing daylength, a variety of media, supplementation with salicylic acid or ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid) (EDDHA), as well as various culture vessels for effects on flowering of verified Lemnaceae strains available from the Rutgers Duckweed Stock Cooperative.

Watermeal, Wolffia australiana, is the smallest known flowering monocot and is rich in protein. Despite its great potential as a biotech crop, basic research on Wolffia is in its infancy. Here, we generated the reference genome of a species of watermeal, W. australiana, and identified the genome-wide features that may contribute to its atypical anatomy and physiology, including the absence of roots, adaxial stomata development, and anaerobic life as a turion. In addition, we found evidence of extensive genome rearrangements that may underpin the specialized aquatic lifestyle of watermeal. Analysis of the gene inventory of this intriguing species helps explain the distinct characteristics of W. australiana and its unique evolutionary trajectory., Halim Park and Jin Hwa Park et al. report the nuclear genome sequence of the duckweed Wolffia australiana, the smallest known flowering plant. The genome assembly represents an improvement over a recently published genome and highlights genome rearrangements that may be linked to its specialized aquatic adaptations.

To colonise other planets, self-sufficiency of space missions is mandatory. To date, the most promising technology to support long-duration missions is the bioregenerative life support system (BLSS), in which plants as autotrophs play a crucial role in recycling wastes and producing food and oxygen. We reviewed the scientific literature on duckweed (Lemnaceae) and reported available information on plant biological traits, nutritional features, biomass production, and space applications, especially of the genus Wolffia. Results confirmed that the smallest existing higher plants are the best candidate for space BLSS. We discussed needs for further research before criticalities to be addressed to finalise the adoption of Wolffia species for space missions.

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on the safety of water lentil powder as a novel food (NF) pursuant to Regulation (EU) 2015/2283. Water lentils refer to aquatic plants belonging to the Araceae family and represented by five genera (Lemna, Wolffia, Wolffiella, Landoltia and Spirodela). The NF is thermally washed and dried water lentils, which are produced as a polyculture crop consisting of species from the Lemna genus (70-100%) and the Wolffia genus (0-30%). The main constituents of the NF are protein, fibre and fat. The Panel notes that the concentration of trace elements and contaminants in the NF is highly dependent on the conditions of cultivation of the plant and the fertiliser composition. The NF is expected to be stable and to comply with the specifications during the suggested shelf life. The NF is intended for human consumption as a food ingredient in herbs, spices and seasonings, sauces, soups and broths, protein products, dietary food for weight control and as a food supplement. The target population is the general population, except for food supplements which are exclusively intended for consumption by adults. The Panel considers that based on the composition of the NF and the proposed intended uses, the NF is not nutritionally disadvantageous, except for the concerns regarding intake of manganese from the NF. No adverse effect was observed in the submitted 90-day subchronic study, at the highest dose, 1,000 mg/kg body weight (bw) per day of NF. The Panel considers that, based on the protein concentration, the consumption of the NF may trigger allergic reactions. The Panel concluded that an increase in manganese intake from the NF used as food ingredient or food supplements is of safety concern and the safety of the NF cannot be established. (C) 2021 European Food Safety Authority. EFSA Journal published by John Wiley and Sons Ltd on behalf of European Food Safety Authority.

Vibriosis is a commonly found bacterial disease identified among fish and shellfish cultured in saline waters. A multitude of Vibrio species have been identified as the causative agents. LamB, a member of outer membrane protein (OMPs) family of these bacteria is conserved among all Vibrio species and has been identified as an efficient vaccine candidate against vibriosis. Rootless duckweed (Wolffia) is a tiny, edible aquatic plant possessing characteristics suitable for the utilization as a bioreactor. Thus, we attempted to express a protective edible vaccine antigen against fish vibriosis in nuclear-transformed Wolffia. We amplified LamB gene from virulent Vibrio alginolyticus and it was modified to maximize the protein expression level and translocate the protein to the endoplasmic reticulum (ER) in plants. It was cloned into binary vector pMYC under the control of CaMV 35S promoter and introduced into Wolffia globosa by Agrobacterium-mediated transformation. Integration and expression of the LamB gene was confirmed by genomic PCR and RT-PCR. Western blot analysis revealed accumulation of the LamB protein in 8 transgenic lines. The cross-protective property of transgenic Wolffia was evaluated by orally vaccinating zebrafish through feeding fresh transgenic Wolffia and subsequently challenging with virulent V. alginolyticus. High relative percent survival (RPS) of the vaccinated fish (63.3%) confirmed that fish immunized with transgenic Wolffia were well-protected from Vibrio infection. These findings suggest that Wolffia expressed LamB could serve as an edible plant-based candidate vaccine model for fish vibriosis and feasibility of utilizing Wolffia as bioreactor to produce edible vaccines.

Wolffia is the fastest growing plant genus on Earth with a recorded doubling time of less than a day. Wolffia has a dramatically reduced body plan, primarily growing through a continuous, budding-type asexual reproduction with no obvious phase transition. Most plants are bound by the 24-hour light-dark cycle with the majority of processes such as gene expression partitioned or phased to a specific time-of-day (TOD). However, the role that TOD information and the circadian clock plays in facilitating the growth of a fast-growing plant is unknown. Here we generated draft reference genomes for Wolffia australiana (Benth.) Hartog & Plas to monitor gene expression over a two-day time course under light-dark cycles. Wolffia australiana has the smallest genome size in the genus at 357 Mb and has a dramatically reduced gene set at 15,312 with a specific loss of root (WOX5), vascular (CASP), circadian (TOC1), and light-signaling (NPH3) genes. Remarkably, it has also lost all but one of the NLR genes that are known to be involved in innate immunity. In addition, only 13% of its genes cycle, which is far less than in other plants, with an overrepresentation of genes associated with carbon processing and chloroplast-related functions. Despite having a focused set of cycling genes, TOD cis-elements are conserved in W. australiana, consistent with the overall conservation of transcriptional networks. In contrast to the model plants Arabidopsis thaliana and Oryza sativa, the reduction in cycling genes correlates with fewer pathways under TOD control in Wolffia, which could reflect a release of functional gating. Since TOD networks and the circadian clock work to gate activities to specific times of day, this minimization of regulation may enable Wolffia to grow continuously with optimal economy. Wolffia is an ideal model to study the transcriptional control of growth and the findings presented here could serve as a template for plant improvement.

The Lemnaceae family, commonly called duckweeds, is 37 species of the smallest and simplest flowering plants found floating on nutrient-rich waters worldwide. Their small size and rapid clonal growth in aseptic conditions made them a stable and simple model for plant research especially from 1950 to 1990, when they were used to study plant physiology and biochemistry including auxin synthesis and sulfur metabolism. Duckweed research then saw a resurgence in 2008 when global fuel prices rose and the US Department of Energy funded the sequencing of the Spirodela polyrhiza genome. This launched not only the genomic investigations detailed in this book, but the regrowth of duckweed industrial applications. Thanks to their ability to quickly absorb nitrogen, phosphorous, and other nutrients while removing pathogens and growing at a rate of 13–38 dry tons/hectare year in water treatment lagoons, scientists are currently exploring ways that duckweed can convert agricultural and municipal wastewater into clean water and a high-protein animal feed. The potential of these plants for phytoremediation of heavy metals and organic compounds also allows the possibility to clean the wastewater from heavy industry while providing biofuels and even plastics. Finally, thanks to their superb nutritional profile Wolffia species grown in clean conditions promise to become one of the healthiest and most environmentally friendly vegetables. Given the importance of these incredible plants, it is no wonder researchers are investigating the genetic mechanisms that make it all possible.

There are five genera (Spirodela, Landoltia, Lemna, Wolffiella and Wolffia) of duckweed species widely distributed in various freshwater habitats worldwide. Rapid growth rate, predominantly asexual reproduction and floating growth made them ideal for a plant model. The sensitivity to some toxicants and enrichment capacity also made duckweeds favorable in biomonitoring and bioremediation in contaminated water. Furthermore, duckweeds have increasingly been considered as alternative sources for bioenergy and food, due to their high biomass accumulation rate and nutritional contents. Both stable and transient transformation protocols have been established for some duckweed species. Agrobacterium-mediated method is the main approach in duckweeds genetic transformation, which could be affected by the type of explants, Agrobacterium strains, their densities, co-culture conditions and antibiotics and their concentrations. Particle treatment and other improvements such as vacuum infiltration can accelerate transient transformation efficiency by microprojectile bombardment method. Inadequacies are still present in genetic transformation of some duckweed species including low efficiency of transformation and long-time period especially using calli as infected materials. Therefore, more concentrated and persistent efforts to develop efficient approaches for genetic transformation of duckweeds are still needed. Furthermore, it is necessary to make an effort to express various types of genes so as to expand the development and utilization of duckweeds.

Duckweeds (family Lemnaceae) comprise 37 angiosperm species, which are distributed among five genera. Although these tiny specimens represent the smallest flowering plants on earth, the group is practically ubiquitous in water bodies worldwide. The paucity of morphological features in duckweeds has made it difficult to elucidate their evolutionary history, or to present a compelling classification of the group, but more recent molecular evidence has facilitated an improved systematic evaluation of these unique plants. The duckweeds are closely related to aroids (family Araceae), with which they share several morphological features. Within Lemnaceae, the two species of Spirodela and the monotypic genus Landoltia are more distantly related to other duckweeds than are the larger genera Lemna, Wolffia, and Wolffiella to one another. A substantial amount of plastid DNA sequence data has upheld a phylogeny for the family that is mostly consistent, and many of those relationships have been corroborated by the recent addition of nuclear DNA data. Morphologically, the genera lacking roots (Wolffia and Wolffiella) comprise a single lineage, as do the three largest genera (Lemna, Wolffia, and Wolffiella) that are more reduced in comparison with Landoltia and Spirodela. The biogeography of Lemnaceae indicates that numerous dispersal events have occurred in relatively recent evolutionary time, and that several species essentially are cosmopolitan. Although not particularly speciose, duckweeds comprise a surprisingly diverse group with much potential for exploring various genetic, biochemical, and metabolic phenomena.

Duckweed is an interesting model for studying cytogenetics, epigenetics and karyotype evolution. Belonging to the monocotyledonous arum or aroid family Araceae, these aquatic plants present an approximately 12-fold range of different genome sizes, from 158 Mbp (Spirodela sps.) to 1881 Mbp (Wolffia arrhiza) and variable chromosome numbers. In addition to reduced gene repertoires that found in so far all published duckweed genomes of Spirodela, Lemna and Wolffia species, several peculiar genome and epigenome features (e.g. the lowest copy number of genes coding for rRNA, extreme levels of global DNA methylation, and atypical patterns of heterochromatic and euchromatic territories) indicate a unique and interesting history of duckweed genome evolution, organization and adaptation to plants with simplified body architecture and extremely fast growth rate. Together with the high-throughput long-read, long-range information and optical mapping technologies, available cytogenetic resources, including an efficient and robust protocol of multicolour fluorescence in situ hybridization (mcFISH) and mitotic chromosome preparation, and a Spirodela genome-integrated bacterial-artificial-chromosome (BAC) map with ancestral chromosome linkages allow further comprehensive comparative genomic and cytogenetic analysis between duckweed, its close relatives, and other monocotyledonous plants of interest.

Duckweeds are the simplest and smallest (“frond” size 1 mm to less than 1 cm) flowering plants, able to grow on fresh and polluted water. In the recent past, intense research to understand various species and their potential has been underway, especially in the genetics and biochemical repertoire. Duckweeds come under the family Lemnaceae and contain genera such as Lemna, Spirodela, Landolita, Wolffia and Wolffella. Duckweeds thrive ubiquitously as autotrophs using photosynthesis to source their nutritional requirements from solar energy and minerals from the rhizosphere. They are also endowed to absorb and accumulate heavy metals, radionucleotides and metalloids with potential for phytoremediation. The metabolic versatility of duckweeds can be deployed as nutrition in aquaculture, livestock and of late as functional foods. Duckweeds are currently being explored to find new applications in feed to complement diets and increase animal growth either alone or coupled with crop residues to bring about a balance of nutrients. Duckweeds have emerged as an important food resource; a case in point is Wolffia arrhiza. Consumed in various formats, duckweeds have a good balance of proteins, fat, starch, an array of favorable amino acids and fatty acids, minerals and antioxidants, phytosterols and much sought after omega-3 fatty acids as well.

Duckweeds include the world's smallest and fastest growing flowering plants that have the capacity to produce huge biomass with a broad range of potential applications like production of feed and food, biofuel and biogas. In order to achieve optimal and sustainable commercial system, it is necessary that suitable species and clones of duckweeds be identified and selected based on appropriate strategies. However, a high degree of reduction in their structural complexity poses serious problems in identification of closely related species of duckweeds, on a morphological basis. Use of molecular taxonomic tools is the present solution. The state of the art of molecular taxonomy of all the five genera of duckweeds (Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia) is based mainly on the techniques of fingerprinting by amplified fragment length polymorphism (AFLP) and barcoding using sequences of plastidic DNA fragments. After more than 15 years of molecular taxonomic investigations, a certain viewpoint is now available demonstrating all five genera to be monophyletic. Also, the phenetic analyses had made huge progress in delineating the currently defined 36 species of duckweeds, although, all species cannot yet be defined with confidence. Wolffiella has turned out to be the most complicated genus as only 6 to 7 species out of the 10 can be reliably delineated. Further progress in the phylogenetic and phenetic analyses requires more advanced methods like next generation and/or whole genome sequencing. First results using the method genotyping-by-sequencing in the genus Lemna (in combination with metabolomic profiling by matrix-assisted laser desorption ionization time-of-flight mass-spectrometry (MALDI-TOF-MS) as well as AFLP and barcoding by plastidic sequences) are more promising: The species Lemna valdiviana and Lemna yungensis were united to one species, Lemna valdiviana. This reduced the total number of Lemnaceae species to 36.

The present Present experiment was conducted for 75 days in triplicates groups in 18 aquaria of 50 L each to study the effect of Wolffia arrhiza and Spirulina platensis on growth and pigmentation of Botia dario. Six isonitrogenous diets were prepared with 350 g/kg crude protein (CP) level. Diet 1 (T1) was prepared without fortification of spirulina and wolffia. T2 diet was prepared with spirulina as supplement of carotenoids. Similarly, T3, T4, T5 and T6 diets were prepared by substituting 25, 50, 75 and 100 g/kg of CP from spirulina with wolffia, respectively. Significant differences (p .05). Thus, it can be concluded that diet containing 100 g/kg spirulina can be effective for better growth while diet containing 25 g/kg spirulina and 150 g/kg wolffia can be effective for higher survival and pigmentation in Botia dario.

Duckweeds have been consumed as human food since long. Species of the duckweed genera, Spirodela , Landoltia , Lemna , Wolffiella and Wolffia were analysed for protein, fat, and starch contents as well as their amino acid and fatty acid distribution. Protein content spanned from 20% to 35%, fat from 4% to 7%, and starch from 4% to 10% per dry weight. Interestingly, the amino acid distributions are close to the WHO recommendations, having e.g. 4.8% Lys, 2.7% Met + Cys, and 7.7% Phe + Tyr. The content of polyunsaturated fatty acids was between 48 and 71% and the high content of n3 fatty acids resulted in a favourable n6/n3 ratio of 0.5 or less. The phytosterol content in the fastest growing angiosperm, W. microscopica, was 50 mg g −1 lipid. However, the content of trace elements can be adjusted by cultivation conditions. Accordingly, W. hyalina and W. microscopica are recommended for human nutrition.

Several of the aquatic plants act as kidneys for amelioration of the toxicity of metals and metalloids (phytoremediation). It is economical and environmentally friendly. Phytoremediation includes several processes rendering the toxic metals and metalloids less toxic. Industrial wastewater contains toxic metals and metalloids, that is, chromium, arsenic, cadmium, lead, zinc, and nickel, which are toxic, carcinogenic, cytotoxic, teratogenic, and mutagenic. Several of the high biomass producing macrophytes such as Azolla filiculoides, Azolla pinnata, Bacopa monnieri, Canna flaccid, Carex praegracilis, Ceratophyllum demersum, Cladium jamaicense, Eichhornia crassipes, Elodea canadensis, Eriophorum angustifolium, Eriophorum scheuchzeri, Glyceria fluitans, Hydrocotyle umbellate, Ipomea aquatica, Iris lacteal, Juncus articulates, Lemna minor, Lemna, Spirodela, Myriophyllum aquaticum, Myriophyllum spicatum, Nymphaea violacea, Phragmites australis, Phragmites sp., Pistia stratiotes, Polygonum punctatum, Potamogeton natans, Potamogeton pectinatus, Potamogeton pusilus, Rumex hydrolapatum, Sagittaria latifolia, Salicornia virginica, Salix alba, Salvinia molesta, Scirpus sp., Scirpus validus, Spartina alterniflora, Spirodela oligorrhiza, Sporobolus virginicus, Tamarix sp., Typha latifolia, Vallisneria Americana, Vallisneria spiralis, Wolffia, Zizania aquatic, etc. are reported remove toxic metals and metalloids including hazardous wastes like cyanide and fluoride from industrial wastewater. Metal tolerance in plants is governed by several factors that render phytoremediation an effective technique. Molecular biology and overexpression of genes for accumulation and detoxification of toxic metals and metalloids resulted in enhanced phytoremediation fostering large-scale application to remediate industrial wastewaters. In this context overexpression of several metal chelators like metallothioneins, phytochelatins, and phytosiderophores. Furthermore, several genes involved in the uptake, transport, sequestration, and modification of heavy metals are being identified. In these chapters the prospects for genetic engineering and transgenic approaches in water weeds for removal of toxic metals and metalloids in industrial wastewaters and development of genetically modified plants for increasing their applicability in addressing the problems of industrial wastewaters are discussed.

A 90 days' trial on integrated multi-trophic aquaculture (IMTA) incorporating floating weed Wolffia globosa as inorganic extractive and a bivalve Lamellidens marginalis as organic extractive was conducted to assess the growth, survival, yield, water quality and welfare of Labeo rohita (Rohu) in an outdoor tank culture system. Twelve cement tanks (20 m3) were randomly allocated into four treatments (in triplicate) where L. rohita was used as fed species. The treatments were assigned as control (C) only rohu, T1: Rohu and partitioned Wolffia canopy, T2: Rohu, L. marginalis and T3: Rohu, Wolffia and L. marginalis. The stocking densities for rohu and L marginalis were 30,000 fingerlings ha−1 and 750 kg ha−1 while Wolffia was transplanted to cover 30% of the tank surface area, and fish to mussel biomass ratio maintained was 2:1. The fish were fed with a sinking pelleted feed (30% Crude Protein) at the rate of 4% body weight. It is observed that total biomass, survival, net fish yield (NFY) was significantly highest in T3 as compared to T1, control and T2. The total protein and lipid content of rohu (whole-body) differ significantly between the treatments. Among the welfare parameters, the nitroblue tetrazolium (NBT) activity was significantly higher in T1 and T3 while superoxide dismutase (SOD) was highest in T1. The catalase (CAT) activity lowest in T3 among all the treatment groups. The water quality parameters like NH4-N, NO3-N, PO4-P were significantly lower in T3 among all treatment groups. Higher water transparency was observed with no algal bloom in T3 and T1. The results suggest that co-culture of L. rohita with W. globosa and L. marginalis can improve water quality, welfare parameters, enhancing fish survival and productivity.

Duckweed farming can be a sustainable practice for biofuel production, animal feed supplement, and wastewater treatment, although large scale production remains a challenge. Plant growth promoting bacteria (PGPB) have been shown to improve plant health by producing phytohormones such as auxin. While some of the mechanisms for plant growth promotion have been characterized in soil epiphytes, more work is necessary to understand how plants may select for bacterial endophytes that have the ability to provide an exogenous source of phytohormones such as auxin. We have isolated and characterized forty-seven potentially endophytic bacteria from surface-sterilized duckweed tissues and screened these bacterial strains for production of indole related compounds using the Salkowski colorimetric assay. Indole-3-acetic acid (IAA), indole-3-lactic acid (ILA), and indole produced by various bacterial isolates were verified by mass spectrometry. Using the Salkowski reagent, we found that 79% of the isolated bacterial strains from our collection may be capable of producing indole related compounds to various extents during in vitro growth. Of these bacteria that are producing indole related compounds, 19% are additionally producing indole. There is an apparent correlation between the type of indole related compound produced by a particular bacteria and the duckweed genus from which the bacterial strain is derived. These results suggest the possible association between different duckweed genera and endophytes that are producing distinct types of secondary metabolites. Understanding the role of indole related compounds during interaction between endophytes and the plant host may be useful to help design synthetic bacterial communities that could target specific or multiple species of duckweed in the future to sustainably enhance plant growth.

To date, the expression of recombinant proteins in transgenic plants is becoming a powerful alternative to classical expression methods. Special efforts are directed to the development of contained cultivation systems based on cell culture or rhyzosecretion, which reliably prevents the heterologous DNA releasing into the environment. A promising object for the development of such systems is the tiny aquatic plant of wolffia (Wolffia arrhiza (L.) Horkel ex Wimm.), which can be used as a dipped culture in bioreactors. Herein we have expressed the human granulocyte colony-stimulating factor (hG-CSF) in nuclear-transformed wolffia. The nucleotide sequence of hG-CSF was optimized for expression in wolffia and cloned into the vector pCamGCSF downstream of double CaMV 35S promoter. Wolffia plants were successfully transformed and 34 independent transgenic lines with hG-CSF gene were obtained, PCR and Southern blot analysis confirmed the transgenic origin of these lines. Western blot analysis revealed accumulation of the target protein in 33 transgenic lines. Quantitative ELISA of protein extracts from these lines showed hG-CSF accumulation up to 35.5 mg/kg of wolffia raw weight (0.194% of total soluble protein). This relatively high yield holds promise for the development of wolffia-based expression system in strictly controlled format to produce various recombinant proteins.

Members of the Wolffia genus are fascinating plants for many biologists as they are the smallest flowering plants on Earth and exhibit a reduced body plan that is of great interest to developmental biologists. There has also been recent interest in the use of these species for bioenergy or biorefining. Molecular and developmental studies have been limited in Wolffia species due to the high genome complexity and uncertainties regarding the stable genetic transformation. In this manuscript we present new protocols for both stable and transient genetic transformation for Wolffia globosa using Agrobacterium tumefaciens. For the transient transformation, we used Wolffia fronds whereas we used clusters for the stable transformation. As proof of concept we transformed two synthetic promoter constructs driving expression of the GUS marker gene, that have previously been used to monitor auxin and cytokinin output in a variety of species. Using these approaches we obtained a Transformation Efficiency (TE) of 0.14% for the stable transformation and 21.8% for the transient transformation. The efficiency of these two methods of transformation are sufficient to allow future studies to investigate gene function. This is the first report for successful stable transformation of W. globosa.

Duckweeds (Lemnaceae family) are the smallest flowering plants that adapt to the aquatic environment. They are regarded as the promising sustainable feedstock with the characteristics of high starch storage, fast propagation, and global distribution. The duckweed genome size varies 13-fold ranging from 150 Mb in Spirodela polyrhiza to 1,881 Mb in Wolffia arrhiza. With the development of sequencing technology and bioinformatics, five duckweed genomes from Spirodela and Lemna genera are sequenced and assembled. The genome annotations discover that they share similar protein orthologs, whereas the repeat contents could mainly explain the genome size difference. The gene families responsible for cell growth and expansion, lignin biosynthesis, and flowering are greatly contracted. However, the gene family of glutamate synthase has experienced expansion, indicating their significance in ammonia assimilation and nitrogen transport. The transcriptome is comprehensively sequenced for the genera of Spirodela, Landoltia, and Lemna, including various treatments such as abscisic acid, radiation, heavy metal, and starvation. The analysis of the underlying molecular mechanism and the regulatory network would accelerate their applications in the fields of bioenergy and phytoremediation. The comparative genomics has shown that duckweed genomes contain relatively low gene numbers and more contracted gene families, which may be in parallel with their highly reduced morphology with a simple leaf and primary roots. Still, we are waiting for the advancement of the long read sequencing technology to resolve the complex genomes and transcriptomes for unsequenced Wolffiella and Wolffia due to the large genome sizes and the similarity in their polyploidy.

For the first time to our knowledge, we demonstrate that whole angiosperm individuals can survive gut passage through birds, and that this occurs in the field. Floating plants of the genus Wolffia are the smallest of all flowering plants. Fresh droppings of white-faced whistling duck Dendrocygna viduata (n = 49) and coscoroba swan Coscoroba coscoroba (n = 22) were collected from Brazilian wetlands. Intact Wolffia columbiana were recovered from 16% of D. viduata and 32% of Coscoroba samples (total = 164 plantlets). The viability of plants was tested, and asexual reproduction was confirmed. Wolffia columbiana is an expanding alien in Europe. Avian endozoochory of asexual angiosperm propagules may be an important, overlooked dispersal means for aquatic plants, and may contribute to the invasive character of alien species.

Duckweeds (Lemnaceae) possess good qualitative and quantitative profiles of nutritional components for its use as human food. However, no studies have been conducted on the probable presence or absence of any adverse effects. The extracts from seven duckweed species (Spirodela polyrhiza, Landoltia punctata, Lemna gibba, Lemna minor, Wolffiella hyalina, Wolffia globosa, and Wolffia microscopica) covering all five genera of the plant family were herewith tested for cytotoxic effects on the human cell lines HUVEC, K-562, and HeLa and for anti-proliferative activity on HUVEC and K-562 cell lines. From these assays, it is evident that duckweeds do not possess any detectable anti-proliferative or cytotoxic effects, thus, the high nutritional value is not diminished by such detrimental factors. The present result is a first step to exclude any harmful effects of highly nutritious duckweed for human.

To date, Lemna and Spirodela species of the family Lemnaceae are the only species that have been used to produce recombinant proteins for pharmaceutical and veterinary purposes. Wolffia arrhiza is the most evolutionarily advanced species of the Lemnaceae. A rootless duckweed, it is the most promising target for biopharmingas a candidate for submerged cultivation in a fermenter. As a first step toward future biotechnological use of Wolffia, we established a stable transformation system for it based on Agrobacterium-mediated transformation. Following inoculation with the bacteria, Wolffia cluster explants were cultured for 2 weeks on media containing 2.0 mg l−1 2,4-dichlorophenoxyacetic acid and 2.0 mg l−1 N6-benzyladenine. Explants were then transferred to growth regulator-free media in the presence of 5.0 mg l−1 hygromycin B to select antibiotic-resistant plants. Other selective agents—kanamycin and phosphinothricin—were not suitable for Wolffia, nor was application of particle bombardment for the delivery of foreign DNA to Wolffia explants. The developed agro transformation conditions yielded stably transformed lines of Wolffia, confirmed by Southern blotting, with an efficiency of 0.2–0.4 % transgenes per 100 explants.

The quest for alternative sources of energy has evoked the interest in exploring potentials of living biological wastes as new energy materials. Duckweeds are produced abundantly as weeds in freshwater surface bodies and can be a source of biomass for bioenergy productions. There are approximately 40 species of this group worldwide belonging to five genera (Spirodela, Lemna, Wolfiella, Wolffia and Landoltia). The structural peculiarities (small plant size, limited life cycle, high duplication rate, etc.) and chemical characteristics (dry weight basis): 17.6–35 % (carbohydrate), 21–38 % (starch), 16–41.7 % (crude protein), 8.8–15.6 % (crude fibre) and 4.5–9 % (lipid) make duckweed as possible feedstock for biomass-based energy operations. The high contents of valuable fatty acids (palmitic acid and linoleic acid) and starch (3–75 %) in duckweed biomass suggest its utility in biorefinery. Recent lab-scale studies have shown remarkable results in terms of energy yield during the processes like anaerobic digestion, incineration, pyrolysis, gasification, oxidation, etc. Another good quality of duckweeds is its hyperaccumulative properties for a variety of water pollutants. Therefore, this group of weeds has been recommended widely for designing on-site phytoremediation system for community wastewater treatment. Thus, duckweed technology can be adopted as coupled technology to harness two environmental approaches, i.e. wastewater treatment and energy biomass production for sustainable development of the human society.

The rediscovered species Wolffia microscopica (Griff.) Kurz, endemic to India, Pakistan and Bangladesh, shows several features that make it unique in comparison to other duckweeds, even to other species of the genus Wolffia. During vegetative propagation, the daughter fronds are produced by budding within a single pouch of the mother frond. Several generations of fronds and their initials exist in union with the parent frond at a given time. Most strikingly, almost all the fronds flower, both in nature and under controlled culture conditions. Thus, in contrast to all other duckweed species, generative propagation is as important as vegetative propagation, which opens the opportunity for artificial breeding. Moreover, flower development on both mother and daughter fronds was observed at the same time. In contrast to all other duckweed species, fronds of W. microscopica often possess a ventral projection of varying length ranging from an almost flat appearance of the ventral surface to a length of 4 mm. Absence of root cap, root hairs and vascular tissue demonstrate that this ventral protrusion is not a root and accordingly we name this special structure “pseudoroot”. The high number of chloroplasts in the pseudoroot may result in higher capacity of photosynthesis without increasing the frond area which covers the water surface. Thus we propose that the pseudoroot serves to be advantageous to W. microscopica in multiplying at a faster rate in comparison to other duckweeds.

A field experiment was conducted in a combinatorial approach to evaluate the performance of five aquatic plants, singly and in all possible combinations of two plants, for As removal from 4 L of 2500 μg L−1 As in 30 days. Under As stress, Hydrilla showed an increase in growth rate (19%) in comparison to control, while other plants demonstrated a decline. Among different combinations, Ceratophyllum + Lemna, Hydrilla + Ceratophyllum and Hydrilla + Wolffia showed higher growth in As (92%, 43%, and 33%, respectively) than under control conditions. Total As removal (μg) in 30 days was found to be the maximum for Ceratophyllum + Lemna (4365) followed by Hydrilla + Ceratophyllum (3326) and Hydrilla + Wolffia (1896). In all combinations of plants, Hydrilla always contributed more than 50%. The study advocates the use of Hydrilla/Ceratophyllum as one plant of choice to be used in combination. It also proposes to screen for different combinations of two of more plants for better application of phytoremediation technology in field.

The diversification of the Lemnoideae was accompanied by a reduction in the abundance of cell wall apiogalacturonan and an increase in xylogalacturonan whereas rhamnogalacturonan II structure and cross-linking are conserved. The subfamily Lemnoideae is comprised of five genera and 38 species of small, fast-growing aquatic monocots. Lemna minor and Spirodela polyrhiza belong to this subfamily and have primary cell walls that contain large amounts of apiogalacturonan and thus are distinct from the primary walls of most other flowering plants. However, the pectins in the cell walls of other members of the Lemnoideae have not been investigated. Here, we show that apiogalacturonan decreased substantially as the Lemnoideae diversified since Wolffiella and Wolffia walls contain between 63 and 88% less apiose than Spirodela, Landoltia, and Lemna walls. In Wolffia, the most derived genus, xylogalacturonan is far more abundant than apiogalacturonan, whereas in Wolffiella pectic polysaccharides have a high arabinose content, which may arise from arabinan sidechains of RG I. The apiose-containing pectin rhamnogalacturonan II (RG-II) exists in Lemnoideae walls as a borate cross-linked dimer and has a glycosyl sequence similar to RG-II from terrestrial plants. Nevertheless, species-dependent variations in the extent of methyl-etherification of RG-II sidechain A and arabinosylation of sidechain B are discernible. Immunocytochemical studies revealed that pectin methyl-esterification is higher in developing daughter frond walls than in mother frond walls, indicating that methyl-esterification is associated with expanding cells. Our data support the notion that a functional cell wall requires conservation of RG-II structure and cross-linking but can accommodate structural changes in other pectins. The Lemnoideae provide a model system to study the mechanisms by which wall structure and composition has changed in closely related plants with similar growth habits.

Symplocarpus renifolius is a member of Araceae family that is extraordinarily diverse in appearance. Previous studies on chloroplast genomes in Araceae were focused on duckweeds (Lemnoideae) and root crops (Colocasia, commonly known as taro). Here, we determined the chloroplast genome of Symplocarpus renifolius and compared the factors, such as genes and inverted repeat (IR) junctions and performed phylogenetic analysis using other Araceae species. The chloroplast genome of S. renifolius is 158,521 bp and includes 113 genes. A comparison among the Araceae chloroplast genomes showed that infA in Lemna, Spirodela, Wolffiella, Wolffia, Dieffenbachia and Colocasia has been lost or has become a pseudogene and has only been retained in Symplocarpus. In the Araceae chloroplast DNA (cpDNA), psbZ is retained. However, psbZ duplication occurred in Wolffia species and tandem repeats were noted around the duplication regions. A comparison of the IR junction in Araceae species revealed the presence of ycf1 and rps15 in the small single copy region, whereas duckweed species contained ycf1 and rps15 in the IR region. The phylogenetic analyses of the chloroplast genomes revealed that Symplocarpus are a basal group and are sister to the other Araceae species. Consequently, infA deletion or pseudogene events in Araceae occurred after the divergence of Symplocarpus and aquatic plants (duckweeds) in Araceae and duplication events of rps15 and ycf1 occurred in the IR region.

The functional feeding groups and diversity of macroinvertebrate communities associated with duckweed mats in the New Years River (two sites) and Bloukrans River (two sites), Eastern Cape province, South Africa, were assessed. Duckweed (Lemnaceae) is a ubiquitous family of floating macrophytes. A total of 41 macroinvertebrate families were collected monthly over a six-month period from February to July 2014. Duckweed biomass in both rivers was highly variable both temporally and spatially. The majority of identified macroinvertebrate taxa were predators and detritivores, with a small percentage of herbivores. An average of approximately 26% of the macroinvertebrate taxa found were from families that include species from more than one functional feeding group. Although overall measures of diversity and ecosystem health (Fisher’s α and Simpson’s index) remained constant over time in the New Years River, significant differences in macroinvertebrate community structure were seen between sites and months on both rivers, with dissimilarity being driven by a larger number of species in the New Years River. This high variability within macroinvertebrate assemblages probably reflects a combination of heterogeneous duckweed distribution, variation in physico-chemistry, opportunistic behaviours of macroinvertebrate predators and/or successional colonisation of duckweed mats.Keywords: detritivores, herbivores, Landoltia, Lemna, predators, Wolffia

Wolffia columbiana is a member of the family Lemnaceae and native to the Americas. In 2013, the first two occurrences of Wolffia columbiana in Europe were found in Germany and the Netherlands. Differentiation between W. columbiana and the rare native W. arrhiza is difficult and a scanning electron microscope (SEM) was used to confirm plant identification. A brief description of both populations of W. columbiana and some identifying characteristics are given. Due to their small size, Wolffia species are easily overlooked in the field and/or misidentified, and thus it seems likely, that even more unknown occurrences of alien Wolffia species might occur in Europe. The remaining known occurrences of putative W. arrhiza should be inspected to check their identity. We hypothesize, that alien W. columbiana might be sometimes overlooked or misidentified as the native W. arrhiza, and thus it may have a more widespread distribution within Europe than thought.

The development of tissue-culture systems in duckweed has been limited to species of the genus Lemna. Here we report on a tissue-culture system (callus induction, callus growth and plant regeneration) for the rootless duckweed Wolffia arrhiza. We developed a two-step procedure for callus induction in Wolffia using Schenk & Hildebrandt (SH) medium containing glucose, mannitol and sorbitol. In the first stage, explants were precultivated in the presence of 5.0 mg l−1 2,4-dichlorophenoxyacetic acid and 0.5 mg l−1 N6-benzyladenine (BA) for 16 weeks. In the second stage, BA was replaced with 12.5 mg l−1 Picloram (PCL) for 4 weeks. The resulting callus could be maintained in vitro for a long time (about 1 year) with a relatively low concentration of PCL (4.0 mg l−1), or used to regenerate whole plants by transferring it to growth regulator-free SH medium. The protocols created for callus induction and regeneration were highly efficient at each stage (with the efficiency of 97 % for callus formation and 78 % for regeneration).

Relative growth rates (RGR), doubling times (DT) and relative weekly yields (RY) of 39 clones (ecotypes) from 13 species representing all five genera of duckweeds were determined under standardised cultivation conditions. RGR ranged overall from 0.153 to 0.519 day(-1) , DT from 1.34 to 4.54 days and RY from 2.9 to 37.8 week(-1) . The RGR and RY data can be compared directly to other published findings to only a limited extent on account of missing clonal designations for and limited accessibility to previously investigated clones, as well as the use of different data denominators. However, they are consistent with the published results of other comparative duckweed studies of similar scope in showing that RGR does not vary primarily at the level of the genus or species, but rather reflects the adaptation of individual clones to specific local conditions. The RGR data support the widely held assumption that duckweeds can grow faster than other higher plants and that they can thus surpass land-based agricultural crops in productivity. Duckweeds are highly promising for the production of biomass for nutrition and energy, but extensive clonal comparison will be required to identify the most suitable isolates for this purpose.

After irradiation with gamma radiation from 60Co, differences were found in the survival rates of Wolffia arrhiza (L.) Wimm., cultured in vitro with different amounts of calcium and magnesium. Radiation doses ranged from 80 to 3000 mC•kg-1. Magnesium and especially calcium increased the resistance of Wolffia to acute radiation. This was expressed by the survival of the plants cultured in mediums supplemented with calcium and magnesium after receiving doses of 1200 and 3000 mC•kg-1 while plants cultured in basic medium already showed absolute mortality (DL 100) at exposition to 800 mC•kg-1. Radiosensitivity of Wolffw arrhiza is high compared with other species from the Lemnaceae family.

Free-floating plant outbreaks have attracted the interest of scientists and managers alike due to their strong effects on ecosystem structure and function in shallow lakes and ponds. I evaluated the roles of nitrogen (N), phosphorus (P), and N:P ratios in driving the dominance of duckweeds (Lemnoideae and Wolffioideae) in survey data from 38 ponds in Michigan, USA. I also conducted a mesocosm experiment manipulating the variables in enclosures in two experimental ponds with floating and submerged plants. Floating plants exhibited nonlinear responses to total N, total P, and N:P in the survey data. Experimentally, N drove the initial growth of floating plants. Later in the experiment, floating taxa composition often shifted from Lemna minor L. to filamentous green algae and Wolffia sp., and the shift was associated with increased pH and submerged plant composition. These results support N controlling floating plants, but complex interactions between nutrients, pH, and primary producer community composition need further study.

Making identifiable herbarium vouchers of the minute aquatic vascular plant duckmeal, Wolffia (Lemnoideae; Araceae) has typically required plants to be preserved in transparent, space-consuming vials that are fragile, difficult to work with, and labourious to prepare. An alternative technique for dry-mounting Wolffia within a layer of transparent, acid-free glue presents a promising alternative. Although the largely water-filled individual plants still compress substantially, this preparation technique results in specimens that retain their colour, size, and, most important, their shape. This greatly enhances the possibility of confident identification and simplifies both specimen preparation and storage.

Resumo Lemnoideae sao consideradas as menores Angiospermas, sendo Wolffia o genero com o menor tamanho de fronde e flores. Sao plantas de dificil interpretacao morfologica e os termos utilizados para descricao sao, em parte, diferentes dos usados para outras plantas. Realizou-se o estudo floristico de Lemnoideae ocorrentes no Parana, entre julho de 2013 e setembro de 2014. Os especimes coletados foram identificados e preparados de acordo com tecnicas especiais de herborizacao e depositados no UPCB e UNOP. Foram registradas seis especies: Landoltia punctata, Lemna minuta, Lemna valdiviana, Spirodela intermedia, Wolffia brasiliensis e Wolffiella oblonga. Tipicamente encontradas em ambientes lenticos, valetas de esgoto e enseadas de rio, no Parana foram encontradas em areas de Floresta Ombrofila Densa, Floresta Ombrofila Mista, Floresta Estacional Semidecidual e resquicios de Cerrado. Abstract Lemnoideae are the smallest Angiosperms, Wolffia is the genus with smallest fronds and flowers. Morphological interpretations are difficult and terms used for description are slightly different from those used for other plants. A survey of Lemnoideae was carried out in Parana between July 2013 and September 2014, the specimens collected were identified and prepared according to special herborization techniques and deposited at UPCB and UNOP herbaria. Six species were found: Landoltia punctata, Lemna minuta, Lemna valdiviana, Spirodela intermedia, Wolffia brasiliensis and Wolffiella oblonga. Typically found in lentic environments, sewage ditches and creeks of the river, in Parana they have been collected in Tropical Rainforest, Araucaria Forest, semideciduous forest and cerrado remnants.

Duckweeds are tiny, free-floating, aquatic green plants commonly found in lentic or slowly moving water bodies. Members of the family Lemnaceae include the world's smallest angiosperms and are commonly known as duckweeds. This family comprises five aquatic genera (i.e., Landoltia , Spirodela , Lemna , Wolffia , Wolffiella ) and 38 member species. Nearly all genera are reported to have phytoremediation potential leading to their extensive utilization as a test organism in toxicity testing in different metal-contaminated municipal and industrial wastewaters. Fast growth, rapid reproduction, microbial and phytoplankton reduction, and high nutrient and metal accumulation potential are the factors that have triggered much of the current research to focus over phytoremediation potential of Lemnaceae plants. Lemna and Spirodela species are more widely investigated for reclamation of municipal and metal contaminated industrial wastewaters compared with Wolffia and Wolffiella . Besides metal accumulation from the wastewaters, Lemnaceae members significantly improve wastewater quality with respect to chemical oxygen demand, biological oxygen demand, total nitrogen, total phosphorus, total suspended salts, electrical conductivity, and total dissolved solids. Exposure to metal concentrations exceeding physiological tolerance limits induces antioxidant enzyme activities, proline, and organic acid synthesis in duckweeds to counter metal toxicity effects. Metal tolerance for different duckweed species vary with the ambient water environmental conditions (i.e., pH, temperature, electrical conductivity, and number and concentration of metals present. Generally, exposure concentration and duration determine duckweed metal uptake and bioaccumulation potential. Safe disposal of metal-contaminated duckweeds is a burning issue, and their management via incineration, carbonization, hydrolyzes, or anaerobic digestion is current need to prevent further contamination of environmental compartments. Wastewater treatment at point pollution sources with duckweed plant species followed by subsequent safe environmental disposal can help to restore ecological equilibria in aquatic and terrestrial habitats that are already at stake by diverse anthropogenic activities.

Background: Duckweed is the common name for Lemnaceae, a plant family consisting of five major genera: Lemna, Spirodela, Wolffia, Wolffiella and Landoltia. They are the world's smallest and simplest flowering plants with a high growth rate under appropriate environmental conditions. Duckweed can be used as a feed source for livestock and poultry, as well as biomass for production of biofuel and recombinant proteins. Over the last 40 years a great deal of research has been published on the use of duckweed to treat wastewater. These plants can recover nutrients, such as nitrogen and phosphorus, and they can also remove or accumulate metals, radionuclides, and other pollutants in their tissues. Methods: A summary of some of the published works done on duckweed species to remediate natural, domestic, industrial and agricultural wastewaters is presented. The potential of these species for phytoremediation is considered and discussed. Results: Certain duckweed species have the ability to grow on wastewaters, making their biomass production an environmentally friendly process. Duckweed has been extensively studied in pilot-studies and in tertiary treatment of municipal and industrial wastewaters, as well as nutrient recovery from swine wastewater. A relevant number of studies concerns the behaviour of duckweed species towards heavy metals and other elements, such as selenium and arsenic. More recently the attention has been also focused on metals, named Rare Earth Elements (REE) and on emerging pollutants (i.e. pharmaceuticals, personal care products, pesticides and surfactants). The phytoremediation ability of duckweed depends on the growth conditions of the species, the type of pollutants and their concentrations. Conclusion: Progress has been made on use of duckweed in phytoremediation. Current knowledge on the removal efficiencies of several pollutants is limited to laboratory experiments and batch systems, rarely on microcosm- or mesocosm-scale. The removal mechanisms involved, the toxicity to plants caused by contaminants, and the influences of certain important environmental parameters are not fully elucidated. Further studies in this area are still needed in order to provide more and better convincing evidence of the remediation performance of larger laboratory-scale, pilot-scale or fullscale of duckweed.

An alum injection system delivered an alum “micro-floc” to an urban pond from 1997 through 2010 to reduce phosphorus from the water and thereby control Wolffia. Phosphorus concentrations in the pond were reduced from 170 μg/L (pretreatment average) to generally

Wolffia Horkel ex Schleid. (Lemnaceae) includes the world's smallest angiosperms. Morphologically, their bodies are extremely simplified, making classification difficult and long-disputed. No reports about the genetic structure of these clonal-dominant aquatic plants have been published until now. In this study, of 247 samples from 42 populations spanning representative locations in China, two chloroplast haplotypes (glo-cp and un-cp) and 66 amplified fragment length polymorphism genotypes were identified. Based on wide sampling, cpDNA haplotypes, and amplified fragment length polymorphism profiles, we found that there are two genetic lineages (glo- and un- lineages) of Wolffia species in China. Genotypic and genetic diversity of Wolffia species are high compared with other clonal plants (Simpson's index, D= 0.97; Nei's diversity, H= 0.1835). Different spatial structure patterns were detected between glo- and un- lineages. Positive autocorrelation at short distances ( 1500 km) were detected within the glo-lineage, but no significant spatial genetic structure was detected beyond 100 km within the un-lineage. Overall, spatial genetic analysis of W. globosa revealed significant autocorrelation within short distances, indicating that restricted gene flow might be one of the most important factors in shaping genetic structure.

Water crisis is one of the most serious problems faced by the world today. Phytoremediation is one of the serious efforts towards sustainability. Macrophyte-based wastewater treatment systems have several potential advantages compared with conventional treatment systems. Duckweeds (Lemna spp., Spirodela spp., Wolffia spp.) are small, green freshwater, free-floating aquatic plants. The primary objective of this work was to analyze the role of duckweeds in organic waste and nutrient removal from domestic wastewater being generated from hostels of Birla Institute of Technology, Mesra, Ranchi (India). Interesting results were obtained in which the BOD value reduced by 94.45% and the level of orthophosphate at the end of the work was found to be reduced by 79.39%. The duckweeds flourished well during the experimental period in the pH range of 7 to 8; it can be said that, other factors remaining favorable, the optimum pH for duckweed growth ranges from 7 to 8. Therefore, it can be concluded that this treatment can be successfully carried out on a large scale. Also, it is a low-cost solution to wastewater treatment problems and could satisfy the discharge standards.