The 3rd International Conference on Research and Applications at Kyoto is a wonderful opportunity for people working on various duckweed projects. The ICDRA is biannually held; the 1st ICDRA 2011 at Chengdu, China, the 2nd ICDRA 2013 at New Brunswick, the USA. “Aquatic Plants” at the Banbury Center, Cold Spring Harbor Laboratory 2009 was a kind of kickoff meeting for duckweed research and applications in new era.
Here I would like to brief the history of duckweed in the scene of Japanese culture. The Japanese islands have a temperate humid climate and large areas of lands have been used for rice production in paddy fields for long time. Then duckweeds have been familiar to people. The Japanese word “Uki-kusa” for duckweed is very “floating weeds”. Duckweed firstly appeared as “floating sands ” in the oldest collection of Japanese poetry that was compiled in the mid-8th century. Thereafter “Uki-kusa” was frequently referenced in Japanese poetry. It was a symbolic representative of “transience” of life and mind due to its floating nature, or it was used in a rhetorical manner to evoke the feeling “melancholy or woeful”. Thus the duckweed was useful as an intermediary in the poetry world, and there were no “scientific” viewpoints on it. In fact, “Uki-kusa” was also called “Nenashi-kusa” meaning weeds without roots, though neither Wolffia nor Wolffiela was in Japan in those days. These were stories in the times that Kyoto was the capital both in name and reality. Moving to the Edo (the old name for Tokyo) period started from the 17th century, natural sciences gradually grew in Japan and botanical interests were developed. Many varieties of crops and flowers were developed in that era of national isolation. Natural history also grew for plants in Japan. Duckweeds were also described in illustrated books of Japanese Flora. Spirodela polyrhiza, Lemna aequinoctialis or L. minor, and L. trisulca were listed in the same section. In our time, L. aequinoctialis is the dominant species that people can observe in Japan and L. trisulca is almost unobservable in nature. After the opening of Japan to the world in the mid-19th century, sciences and technologies have been dramatically developed. By the end of the 19th century, duckweeds in Japan were described in international journals by Japanese botanists and Landoltia punctata (Spirodela oligorhyza) and Wolffia microscopica were listed as non-native duckweeds in addition. Since then, duckweeds have become plant materials for physiological researches. Flower induction and growth regulation by chemical and physical cues were intensively studied using several Lemna plants from the mid-20th century. Today not only for basic physiologies but for applied technologies, duckweeds become important tools in Japan. Base on these backgrounds, duckweeds have been a familiar teaching material of the plant science in schools from elementary school to college.
This history of duckweed in a bit fortunate background is just the case in Japan. The popularity of duckweed in a country might depend on geometric conditions and cultural factors. However, now duckweed is getting to be a modern model plant with a wide range of applications. Based on the long history of duckweed usages for basic and applied sciences and also for trials to solve environmental and industrial problems, recent progress in the development of experimental tools like genetic transformation, genome editing, mass cultivation and also in the accumulation of genomic, systematic, ecological information is surely spreading “the duckweed fields”. I expect this conference to accelerate the usages of this model plant in various manners.
Graduate School of Science
(Last Update; June 25, 2015)