Genetic structure of the genus Lemna L. (Lemnaceae) as revealed by amplified fragment length polymorphism.

Duckweeds (Lemnaceae) are extremely reduced in morphology, which made their taxonomy a challenge for a long time. The amplified fragment length polymorphism (AFLP) marker technique was applied to solve this problem. 84 clones of the genus Lemna were investigated representing all 13 accepted Lemna species. By neighbour-joining (NJ) analysis, 10 out of these 13 species were clearly recognized: L. minor, L. obscura, L. turionifera, L. japonica, L. disperma, L. aequinoctialis, L. perpusilla, L. trisulca, L. tenera, and L. minuta. However, L. valdiviana and L. yungensis could be distinguished neither by NJ cluster analysis nor by structure analysis. Moreover, the 16 analysed clones of L. gibba were assembled into four genetically differentiated groups. Only one of these groups, which includes the standard clones 7107 (G1) and 7741 (G3), represents obviously the "true" L. gibba. At least four of the clones investigated, so far considered as L. gibba (clones 8655a, 9481, 9436b, and Tra05-L), represent evidently close relatives to L. turionifera but do not form turions under any of the conditions tested. Another group of clones (6745, 6751, and 7922) corresponds to putative hybrids and may be identical with L. parodiana, a species not accepted until now because of the difficulties of delineation on morphology alone. In conclusion, AFLP analysis offers a solid base for the identification of Lemna clones, which is particularly important in view of Lemnaceae application in biomonitoring.