How fast can angiosperms grow? Species and clonal diversity of growth rates in the genus Wolffia (Lemnaceae)

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.