After the genome sequencing of duckweed – how to proceed with research on the fastest growing angiosperm?

There is hardly any need to explain why the production of plant biomass is of increasing importance for the future of our globe (Campbell 2013). It has long been known that duckweeds (Lemnaceae) are suitable for producing large amounts of biomass without competing with the agricultural land that is increasingly required for the production of food plants (Hillman & Culley 1978). A chapter of nearly 40 pages on ‘Application and Economic Importance’ can be found in the duckweed monograph published over a quarter of a century ago (Landolt & Kandeler 1987). This chapter provided a broad overview of the uses of the plant family, and the authors were aware of the great economic potential of duckweeds. However, at that time not even they could envision the current interest in the little plants, particularly as a source of biofuel or biogas. There seems little doubt that given Elias Landolt0s knowledge of the biology of these organisms, and his common sense conservation concerns, that he could have provided valuable perspectives on the economic use of duckweeds well into the future. The most basic, and in one sense most important, contribution Elias Landolt made with his studies of duckweeds was his thorough understanding and appreciation of the biological and evolutionary complexity of the group. There have been very few other such detailed investigations over decades of a taxonomic group of comparable size, in which an investigator has seen all the species in their native habitats as well as in cultivation. It can be validly argued that with so few morphological characters to study in such reduced, miniaturised flowering plants, detailed dedicated studies using additional sources of data were necessary to infer evolutionary relationships. Elias Landolt’s rare combination of keen eye, patience and curiosity led to the amazing insights he achieved in understanding variation and relationships in duckweeds. The two-volume monograph of Lemnaceae (Landolt 1986; Landolt & Kandeler 1987) has to be seen to be appreciated, the two volumes are an amazing compilation of just about everything known about the family at the time, including use of duckweeds in developmental and physiological studies. More than 3,500 references are cited! Someone with such a taxonomic mastery of the duckweeds could simply have been satisfied with knowing more than anyone else about his little creatures; in other words, he could have been content with universal recognition as the world authority on the group. However, as noted above, Elias Landolt was curious about Lemnaceae in a much broader context than their taxonomy. Part of this curiosity was manifested by his desire to collaborate with others in order to learn more about the duckweeds. For example, while he presented intuitive phylogenies for the duckweeds in his monograph, he was eager to have his hypotheses tested with more ‘modern’ methods (Les et al. 2002; Bog et al. 2010, 2013), and he really didn’t care whether or not the data supported his ideas: in the true scientific spirit, he just wanted to understand. Although it should be obvious, it is nevertheless important to emphasise that in these collaborations Elias Landolt was generously providing material for other investigators worldwide from the extensive culture collection he maintained in Zurich for many years. It is difficult to overstate the time, effort and expense that went into obtaining and maintaining that material, not to mention the value of his expertise in attaching names to the material. Clearly, in all collaborations, he was the key person because he not only supplied the material, but he interpreted the results within the broad context of his knowledge of the organisms. It should be mentioned that, almost without exception, collaborative studies supported his taxonomic–phylogenetic concepts in Lemnaceae (Borisjuk et al. 2015; Tippery et al. 2015). The systematic collection and typing of several thousand defined duckweed strains for more than 50 years by Elias Landolt provided an incomparable resource to the community. Dr. Landolt’s generous attitude in sharing this resource and his knowledge of duckweeds also facilitated the development of systematics and biogeographic studies of the family, as well as an annotated source of plant material for a myriad of experimental studies. Indeed, several of the papers in this special issue cite Landolt collections as the sources of experimental material. Both his collection and his taxonomic expertise, combined with his readiness to share his resources with the duckweed community, laid the foundation for the current activity using duckweeds for basic and applied research. This activity is documented through the first International duckweed meetings in Chengdu, China, in 2011 and New Brunswick, New Jersey, in 2013 (Zhao et al. 2012; Lam et al. 2014). The physiological basis of the attractiveness of duckweeds as experimental organisms and for applications is mainly the very rapid vegetative growth rate of many of the 37 species of the family. It has been shown for the first time that duckweed clones represent the fastest growing of all flowering plants (Ziegler et al. 2015; see also the review of Kutschera & Nikals 2015). Interestingly, the variation in growth rates was demonstrated to be primarily at the clonal level (i.e. locally-adapted ecotypes) and not at the species level. The rapid production of biomass by duckweeds, together with the very small genome size in Spirodela polyrhiza (158 Mb; Wang et al. 2011; Wang & Messing 2015), were the reasons for selecting one clone (7498; Durham, NC, USA) for genome sequencing (Wang et al. 2014a,b). Genomic sequence data of another clone of Spirodela polyrhiza (9509; Jena, Germany) had previously been obtained, and a similar quality of