Genomic relationships among diploid and polyploid species of the genusLudwigiaL. sectionJussiaeausing a combination of molecular cytogenetic, morphological, and crossing investigations

The genusLudwigiaL. sectionJussiaeais composed of a polyploid species complex with 2x, 4x, 6x and 10x ploidy levels, suggesting possible hybrid origins. The aim of the present study is to understand the genomic relationships among diploid and polyploid species in the section Jussiaea. Morphological and cytogenetic observations, controlled crosses, genomicin situhybridization (GISH), and flow cytometry were used to characterize species, ploidy levels, ploidy patterns, and genomic composition across taxa. Genome sizes obtained were in agreement with the diploid, tetraploid, hexaploid, and decaploid ploidy levels. Results of GISH showed that progenitors ofLudwigia stolonifera(4x) wereLudwigia peploidessubsp.montevidensis(2x) andLudwigia helminthorrhiza(2x), which also participated for one part (2x) to theLudwigia ascendensgenome (4x).Ludwigia grandiflorasubsp.hexapetala(10x) resulted from the hybridization betweenL. stolonifera(4x) andLudwigia grandiflorasubsp.grandiflora(6x). One progenitor ofL. grandiflorasubsp.grandiflorawas identified asL. peploides(2x). Our results suggest the existence of several processes of hybridization, leading to polyploidy, and possibly allopolyploidy, in the section Jussiaea due to the diversity of ploidy levels. The success of GISH opens up the potential for future studies to identify other missing progenitors inLudwigiaL. as well as other taxa.