Triploids can play an important role in polyploid evolution. However, their frequent sterility is an obstacle for the origin and establishment of neotetraploids. Here we analyzed the microsporogenesis of triploids (x = 7) and the crossability among cytotypes of Turnera sidoides, aiming to test the impact of triploids on the origin and demographic establishment of tetraploids in natural populations. Triploids of T. sidoides exhibit irregular meiotic behavior. The high frequency of monovalents and of trivalents with non-convergent orientations results in unbalanced and/or non-viable male gametes. In spite of abnormalities in chromosome pairing and unbalanced chromosome segregation, triploids are not completely sterile and yielded up to 67% of viable pollen. Triploids that originated by the fusion of 2n × n gametes of the same taxon showed more regular meiotic behavior and higher fertility than triploids from the contact zone of diploids and tetraploids or triploids of hybrid origin. The reproductive isolation of T. sidoides cytotypes of different ploidy level is not strict and the 'triploid block' may be overcome occasionally. Triploids of T. sidoides produce diploid and triploid progeny suggesting that new generations of polyploids could originate from crosses between triploids or from backcrosses with diploids. The capability of T. sidoides to multiply asexually by rhizomes, would enhance the likelihood that a low frequency of neopolyploids can be originated and maintained in natural populations of T. sidoides.

Cytogeographical variability among 564 plants from 26 populations of Turnera sidoides subsp. pinnatifida in mountain ranges of central Argentina was analysed with meiotic chromosome counts and flow cytometry and is described at regional and local scales. Populations were primarily tetraploids (2n = 4x = 28), although diploid (2n = 2x = 14), hexaploid (2n = 2x = 42), and mixed populations of diploids and triploids (2n = 3x = 21) were also found. Diploids, triploids, and hexaploids were fewer in number and restricted to narrow areas, while tetraploids were the most common and geographically widespread cytotype. Diploids grew at higher altitudes and in colder and wet locations; tetraploids had the broadest ecological spectrum, while hexaploids occurred at the lowest altitudes and in drier conditions. The cytotypes were also spatially segregated at a microgeographical scale. Diploids grew in the piedmont, tetraploids were in the adjacent valley, and in the contact zone of both cytotypes, patches of diploids and triploids were found. At a regional scale, the distribution of the cytotypes may be governed by a combination of ecological and historical variables, while segregation in the contact zone may be independent of the selective environment because the cytotypes are unable to coexist as a result of reproductive exclusion. The role of triploids is also discussed.

We set out to identify areas of endemism (AEs) among vascular plants in the Southern Cone of South America, using the genus Senecio (Asteraceae) as proxy. The use of a proxy allows a large-scale study to be carried out in a relatively short time and is suitable for pinpointing areas of interest for further investigation. Senecio is the most obvious choice for a proxy in the Southern Cone, because it is the most diverse genus in the region. We analysed the distribution of 200 endemic species using an optimality criterion (VNDM program). In general, endemism of Senecio in the Southern Cone forms 16 AEs that coincide with previously defined AEs and/or with distribution patterns also supported in phylogeographical studies. As such, Senecio appears to be a suitable proxy in endemicity studies, bearing in mind that these species are of young ages and therefore identify neoendemic AEs. Senecio distribution patterns in the Southern Cone corroborate that high Andean environments are prime sites for endemism, which peaks in the Cuyan High Andean AE, an AE that was not identified in previous endemism studies. Nevertheless, towards the south, the ecotone between the Patagonian Steppe and the Southern Andean forest becomes equally important for speciation.

In order to identify concordant distributions of endemic vascular plants in the Monte desert, we analyzed the distributional data of 180 species endemic to the Monte desert with the optimality criterion implemented in the program VNDM. We detected 13 partially overlapping areas of vascular plant endemism.The main areas of endemism are distributed from north to south associated with the mountainous region of the Precordillera of the Andes towards the west of the study region. These main areas correspond to environments with important variation in elevation and aridity, whereas minor areas correspond to patches of the steppe vegetation towards the east of the study region. We also obtained extensive areas covering much of the Monte desert, coincident with the two classical biogeographic units proposed.  In agreement with the general arid climate of the Monte, most of the endemic flora inhabits arid and/or semiarid environments.

Turnera sidoides (x=7) is one of the few well-studied South American autopolyploid complexes. Since polyploidy has played a prominent role within this complex, ongoing studies in T. sidoides focus on understanding the mechanisms involved in the origin and the establishment of polyploids using integrative approaches. This paper synthesises the results of more than 20 years of research on this topic. Cytogenetics analysis provided evidences for the production of unreduced male and female gametes, supporting the hypothesis of bilateral sexual polyploidization as the mechanism of origin of polyploids in T. sidoides. The finding of viable triploids suggested that unilateral sexual polyploidization could also be an important mechanism for the origin of tetraploids in T. sidoides. The occurrence of plants continuously forming many unreduced gametes would play a key role in the establishment of neopolyploids in natural populations. Also, the higher number of propagules that tetraploids contribute to subsequent generations, the ability to multiply asexually by rhizomes, and the occurrence of occasional cases of self-compatibility and successful illegitimate crosses in polyploids increase the likelihood that a low frequency of neopolyploids can be maintained in natural populations of T. sidoides. In addition, integration of cytogeographic and genetic divergence data together with past niche modelling provided further insights supporting the hypothesis that historical climatic and geomorphological events provided favourable conditions for the establishment of autopolyploids, with the wider distribution of tetraploids of T. sidoides being the result of their range expansion. Key words: cytogeography, establishment, origin, polyploidy, unreduced gametes