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<p><i>Jatropha excisa</i> is found throughout the Chaco phytogeographical province in Argentina, Bolivia, and Paraguay, but its taxonomic boundaries are unclear. This study investigates whether <i>J. excisa</i> comprises more than one species, examining genetic variation and morphological traits, its genetic diversification over time, its native or introduced status in the Chaco, and its distinctiveness from <i>J. gossypiifolia</i>. We analyzed nuclear (ITS) and chloroplast (<i>trn</i>L-<i>trn</i>F) genes from 52 individuals across 32 locations. The results revealed 12 nuclear alleles grouped into four clusters and 29 chloroplast haplotypes with no clear geographic structure. Phylogenetic analysis identified four major clades diverging between 1.8 and 8.1 million years ago, with one clade corresponding to <i>J. excisa</i> and another to <i>J. thyrsantha</i>, indicating at least two distinct species. The findings suggest an ancient divergence among allele groups and a slow geographic expansion of <i>J. excisa</i> over the last 150,000&#xa0;years. This research supports recognizing <i>J. excisa</i> as a distinct native species in the Chaco, diverging from <i>J. gossypiifolia</i> around 18 million years ago, and emphasizes the need for further studies on hybridization and genetic flow among <i>Jatropha</i> species for conservation efforts.</p>

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Phylogeography and specific boundaries of Jatropha excisa (Euphorbiaceae) in the Chaco

  • 期刊论文

  • 发表日期：

    2026年7月22日

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  • Franco E. Chiarini,
  • Raúl E. González-Ittig

摘要

Jatropha excisa is found throughout the Chaco phytogeographical province in Argentina, Bolivia, and Paraguay, but its taxonomic boundaries are unclear. This study investigates whether J. excisa comprises more than one species, examining genetic variation and morphological traits, its genetic diversification over time, its native or introduced status in the Chaco, and its distinctiveness from J. gossypiifolia. We analyzed nuclear (ITS) and chloroplast (trnL-trnF) genes from 52 individuals across 32 locations. The results revealed 12 nuclear alleles grouped into four clusters and 29 chloroplast haplotypes with no clear geographic structure. Phylogenetic analysis identified four major clades diverging between 1.8 and 8.1 million years ago, with one clade corresponding to J. excisa and another to J. thyrsantha, indicating at least two distinct species. The findings suggest an ancient divergence among allele groups and a slow geographic expansion of J. excisa over the last 150,000 years. This research supports recognizing J. excisa as a distinct native species in the Chaco, diverging from J. gossypiifolia around 18 million years ago, and emphasizes the need for further studies on hybridization and genetic flow among Jatropha species for conservation efforts.