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Hybridization plays a fundamental role in plant evolution and diversification, promoting gene flow, morphological novelties, and plant speciation. Here, we integrated fieldwork, collections-based research, morphological observations, molecular systematics, and cytogenetic data to investigate the identity of a previously unidentified taxon of Opuntia (the prickly pear cacti) observed in the north-east region of Argentina, southern South America. Our analyses revealed a cytonuclear phylogenetic discordance among nuclear and plastid genomes, as well as a polyploid nature of the studied taxon. Combining our molecular phylogenetic and cytogenetic analyses with morphological observations, we suggest that hybridization events between the native Opuntia rioplatensis and the North American introduced species, O. ficus-indica, likely produced the taxon here described as O. �� cristalensis. Opuntia is the most widespread genus of Cactaceae, and many species have been introduced worldwide for an array of different purposes. Our report proposes the putative first hybridization event in Opuntia between a North American species with a southern South American lineage, which may shed light on more complex evolutionary scenarios, speciation within the group, and the impacts of species introduction.

El bosque de tres quebrachos en el SO de la Provincia de Chaco es un tipo de bosque poco estudiado y muy afectado por la expansión agropecuaria. Se estudió la composición, la estructura y el estado de conservación de la comunidad de plantas leñosas de los fragmentos remanentes. A partir de 60 parcelas distribuidas en 16 fragmentos (entre 5 y >1000 ha) se determinó la riqueza y la composición especíºca de la comunidad y el área basal y la densidad de cada una de las especies. Se detectaron 36 especies leñosas, todas ellas nativas, con un área basal de 24.73 m2/ha y una densidad de 13459 individuos/ha. Entre las especies del estrato superior se encontró una codominancia entre Schinopsis balansae y Aspidosperma quebracho blanco. Para evaluar el estado de conservación se compararon los resultados obtenidos con datos publicados para quebrachales en áreas protegidas de otras subregiones del Chaco argentino. Se encontró una notable similitud tanto en la riqueza como en los parámetros estructurales. El análisis de los tocones sugiere que la extracción selectiva no es de gran intensidad. Estas observaciones reflejarían un estado de conservación del bosque de tres quebrachos que resulta sorprendentemente bueno si se tiene en cuenta su alto grado de fragmentación. The otres quebrachosp forests in the SW Province of Chaco was scantily studied and strongly affected by the advance of the agricultural frontier. We studied the composition, structure and state of conservation of the woody plant community in remnants fragments. We determined the species richness and the community composition, and basal area and density of each woody species sampling 60 plots distributed in 16 forest fragments (between 5 and >1000 ha). We detected 36 species (trees and shrubs), all of them native. Considering all species together, the mean basal area for all sites was of 24.73 m2/ha, and the density of 13459 individuals/ha. We found a codominance between Schinopsis balansae and Aspidosperma quebracho-blanco among the species of the upper strata. The stumpms analysis showed that selective extraction is limited and it does not imply a strong alteration of the forest structure. To assess the conservation status of these forests, results were compared with published data for other quebracho forests of protected areas from other subregions of the Argentine Chaco. We found a remarkable similarity in the richness and structural parameters of the community. Considering the severe fragmentation of otres quebrachosp forests, our results reflect a surprisingly satisfactory state of conservation. It is necessary to design and implement management strategies to ensure the conservation of this environment.