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.

Ten of 34 tested duckweed clones showed relatively higher salt tolerance. Salinity stress induced high level of starch accumulation in these clones, making them potential feedstock candidates for biofuel production. Duckweeds are promising as a new generation of crop plants that requires minimal input while providing fast biomass production. Two important traits of interest that can impact on the economic viability of this system are their sensitivity to salt and the starch content of the harvested duckweed. We have surveyed 33 strains of duckweed selected from across all 5 genera and amongst 13 species to quantify the natural variance of these traits. We found that there are large ranges of intraspecific variations in salt tolerance, while all species examined accumulated more starch in response to the initial stages of salt stress. However, the magnitude of the change in starch content varied widely between strains. Our results suggest that specific duckweed clones can be cultivated under relatively saline conditions, while increasing salt in the medium before harvesting could be used to increase starch in duckweed biomass for bioethanol production.