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Species of the genus Wolffia are traditionally used as human food in some of the Asian countries. Therefore, all 11 species of this genus, identified by molecular barcoding, were investigated for ingredients relevant to human nutrition. The total protein content varied between 20 and 30% of the freeze-dry weight, the starch content between 10 and 20%, the fat content between 1 and 5%, and the fiber content was ~25%. The essential amino acid content was higher or close to the requirements of preschool-aged children according to standards of the World Health Organization. The fat content was low, but the fraction of polyunsaturated fatty acids was above 60% of total fat and the content of n-3 polyunsaturated fatty acids was higher than that of n-6 polyunsaturated fatty acids in most species. The content of macro- and microelements (minerals) not only depended on the cultivation conditions but also on the genetic background of the species. This holds true also for the content of tocopherols, several carotenoids and phytosterols in different species and even intraspecific, clonal differences were detected in Wolffia globosa and Wolffia arrhiza. Thus, the selection of suitable clones for further applications is important. Due to the very fast growth and the highest yield in most of the nutrients, Wolffia microscopica has a high potential for practical applications in human nutrition.

Rootless plants in the genus Wolffia are some of the fastest growing known plant on Earth.Wolffia have a reduced body plan, primarily multiplying through a budding-type of asexual reproduction. Here we generated draft reference genomes for Wolffia australiana (Benth.) Hartog & Plas, which has the smallest genome size in the genus at 357 Mb and has a reduced set of predicted protein-coding genes at about 15,000. Comparison between multiple high-quality draft genome sequences from W. australiana clones confirmed loss of several hundred genes that are highly conserved amongst flowering plants, including genes involved in root developmental and light signaling pathways. Wolffia has also lost most of the conserved NLR genes that are known to be involved in innate immunity, as well as those involved in terpene biosynthesis, while having a significant overrepresentation of genes in the sphingolipid pathways that may signify an alternative defense system. Diurnal expression analysis revealed that only 13% of Wolffia genes are expressed in a time-of-day (TOD) fashion, which is less than the typical ~40% found in several model plants under the same condition. In contrast to the model plants Arabidopsis and rice, many of the pathways associated with multi-cellular and developmental processes are not under TOD control in W. australiana, where genes that cycle the condition tested predominantly have carbon processing and chloroplast-related functions. The Wolffia genome and TOD expression dataset thus provide insight into the interplay between a streamlined plant body plan and optimized growth.

The aquatic Lemnaceae family, commonly called duckweed, comprise some of the smallest and fastest growing angiosperms known on Earth. Their tiny size, rapid growth by clonal propagation, and facile uptake of labeled compounds from the media were attractive features that made them a well-known model for plant biology from 1950-1990. Interest in duckweed has steadily regained momentum over the past decade, driven in part by the growing need to identify alternative plants from traditional agricultural crops that can help tackle urgent societal challenges such as climate change and rapid population expansion. Propelled by rapid advances in genomic technologies, recent studies with duckweed again highlight the potential of these small plants to enable discoveries in diverse fields from ecology to chronobiology. Building on established community resources, duckweed is re-emerging as a platform to study plant processes at the systems level and to translate knowledge gained for field deployment to address some of society’s pressing needs. This review details the anatomy, development, physiology, and molecular characteristics of the Lemnaceae to introduce them to the broader plant research community. We highlight recent research enabled by Lemnaceae to demonstrate how these plants can be used for quantitative studies of complex processes and for revealing potentially novel strategies in plant defense and genome maintenance.

Lemnaceae, commonly called duckweeds, comprise a diverse group of floating aquatic plants that have previously been classified into 37 species based on morphological and physiological criteria. In addition to their unique evolutionary position among angiosperms and their applications in biomonitoring, the potential of duckweeds as a novel sustainable crop for fuel and feed has recently increased interest in the study of their biodiversity and systematics. However, due to their small size and abbreviated structure, accurate typing of duckweeds based on morphology can be challenging. In the past decade, attempts to employ molecular barcoding techniques for species assignment have produced promising results; however, they have yet to be codified into a simple and quantitative protocol. A study that compiles and compares the barcode sequences within all known species of this family would help to establish the fidelity and limits of this DNA-based approach. In this work, we compared the level of conservation between over 100 strains of duckweed for two intergenic barcode sequences derived from the plastid genome. By using over 300 sequences publicly available in the NCBI database, we determined the utility of each of these two barcodes for duckweed species identification. Through sequencing of these barcodes from additional accessions, 30 of the 37 known species of duckweed could be identified with varying levels of confidence using this approach. From our analyses using this reference dataset, we also confirmed two instances where mis-assignment of species has likely occurred. Potential strategies for further improving the scope of this technology are discussed.

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Species of the genus Wolffia (duckweed) are harvested from natural water bodies in many countries for human consumption. Relative growth rates (RGR) of 25 clones (ecotypes) representing all 11 species of the genus Wolffia were investigated under standardized laboratory conditions in search for potential candidates for production of Wolffia biomass at a biotechnological scale. This is the first report of large-scale screening of physiological properties of Wolffia species. Large differences in RGR of different clones were detected, e.g., in Wolffia globosa. Interestingly, intraspecific differences, i.e., at the level of clones are much higher than differences between species. Rate of photosynthesis (oxygen production in light) and respiration (oxygen consumption in dark) in clones of W. globosa, measured under standardized conditions, are in positive correlation with their respective RGR. Higher rate of photosynthesis seems to be a determining factor for higher RGR. The RGR of the first available axenic clone of the re-discovered species, Wolffia microscopica (clone 2005), depends strongly on the nutrient medium used, in contrast to other investigated species. This clone of W. microscopica has a doubling time of 29.3 h and represents the fastest growing flowering plant known till date.

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