Allopolyploidy and genomic differentiation in holocentric species of the Eleocharis montana complex (Cyperaceae)

Polyploidy and hybridization are key events in plant evolution. Due to these events, complexes of species can be formed. Dysploidy, a frequent chromosome change in holocentric organisms, may add some difficulties to species delimitation, especially in Cyperaceae. The Eleocharis montana complex is known for its members with overlapping morpho-anatomical features and unclear circumscription. To understand its biological history, several tools were used to investigate different American populations, including morpho-anatomical analysis, genome size estimates, cytogenomic analysis, molecular marker characterization, and genomic in situ hybridization (GISH). Despite overlapping morphological features, it was possible to separate two groups, the first containing E. parodii and E. subarticulata, presenting diploid and dysploid karyotypes, respectively, and small DNA C-values. The second contained E. elegans, E. contracta, and E. montana, with large genomes created by polyploidy. All analyses suggest that E. montana with 2n = 40 is a cytotype of E. contracta with 2n = 20, and both evolved from a natural hybridization involving E. parodii (2n = 10) and a second progenitor that is yet unknown. Furthermore, the GISH results indicated that E. parodii may be an ancestor of E. elegans. All species occur in the probable center of diversification in Austral South America, where the hybridization zone is identified. Fieldwork and information obtained from herbaria indicate that diploid and dysploid species (E. subarticulata and E. parodii) do not occur beyond the center of diversification. However, E. elegans and specially E. montana occur more widely, occupying different flooded environments and landscapes.