Summary: Aiming to assess the usefulness of population genetic studies in the identification ofSchizachyriumspecies and the role of natural hybridization in the evolution of these species, the genetic variability and structure ofS. bimucronatum,S. sanguineumandS. tenerumwere analyzed. The identification of unique RAPD bands and cpDNA haplotypes, together with PCoA and AMOVA results, showed that these species differ genetically from each other. The consistency of these results with previously defined morphological groups suggests that population genetic analyses combining nuclear and chloroplast markers would contribute unambiguously to the identification ofSchizachyriumspecies. Furthermore, the finding of some individuals with a proportion of their genomes assignable to those of other populations or species suggests the occurrence of hybridization followed by introgression or polyploidization events. Finally, the patterns of genetic structuring observed may be related to the characteristics of the reproductive systems of the species studied, while the identification of independent evolutionary units in these species would be of interest for the development of conservation strategies for the species and the communities they belong to.

Resumen: A fin de evaluar la utilidad de los estudios genético-poblacionales en la identificación de especies deSchizachyriumy en el papel de la hibridación natural en la evolución de dichas especies,se analizó la variabilidad y estructura genética deS. bimucronatum,S. sanguineumyS. tenerum. La identificación de bandas RAPDs y haplotipos de ADNcp exclusivos, sumados a los resultados del PCoA y AMOVA evidenciaron que dichas especies difieren genéticamente entre sí. La consistencia de estos resultados con la distinción de grupos morfológicos definidos previamente, sugiere que los análisis genético-poblacionales basados en marcadores nucleares y de cloroplastos combinados podrían contribuir a la identificación inequívoca de las especies deSchizachyrium. Asimismo, el hallazgo de algunos individuos con una proporción de sus genomas asignable a los de otras poblaciones o especies, sugiere la ocurrencia de eventos de hibridación seguida de introgresión o de poliploidización. Finalmente, los patrones de estructuración genética observados estarían relacionados a las características de los sistemas reproductivos de las especies estudiadas; mientras que la identificación de unidades evolutivas independientes en dichas especies sería de interés para el desarrollo de estrategias de conservación de las especies y de las comunidades que integran.

Abstract The lowlands of mid-latitude South America comprise complex temperate ecoregions characterized by a unique biodiversity. However, the processes responsible for shaping its species diversity are still largely unknown. Turnera sidoides subsp. carnea is a variable subspecies occurring in the lowlands of northeastern Argentina and Uruguay, extending to southern Paraguay and Brazil. It constitutes a good model to perform evolutionary studies. Here we used an integrative approach to understand the process of diversification within this subspecies and to increase the knowledge concerning patterns and processes responsible for shaping the species diversity in the temperate lowlands of South America. The results provided strong evidences that this subspecies is an autopolyploid complex per se, being in an active process of intrasubspecific diversification. Morphological and genetic data show that the diversity of T. sidoides subsp. carnea is in congruence with the great past and present abiotic and biotic variability of the mid-latitude South American lowlands. The evolutionary history of this subspecies is consistent with past fragmentation and allopatric differentiation at diploid level. Geographic isolation and local adaptation would have promoted strong morphological, ecological, and genetic differentiation, resulting in two morphotypes and different genetic groups indicative of incipient speciation.