Integrative assessment of genetic diversity and micromorphological traits in the widely distributed species Croton urucurana (Euphorbiaceae)

Abstract

Croton urucurana is a pioneer species used in soil regeneration and traditional medicine. Despite expectations of adaptive variation across its extensive range, the species’ macro-geographic genetic structure and its relationship with phenotypic traits are still poorly understood. To address this knowledge gap and identify critical evolutionary reservoirs, this study integrated molecular, anatomical, and palynological data to evaluate diversity across the Chaco, Amazon, Cerrado, and Atlantic Forest domains. Twenty-nine specimens were analyzed using Light and Scanning Electron Microscopy, in parallel to DNA analysis, to assess genetic structure. The study identified two distinct genetic lineages. Brazil exhibited the highest genetic diversity, containing representatives of both lineages. Argentina showed the lowest diversity, composed almost exclusively of a single lineage, whereas Paraguayan samples are distributed between two groups, consistent with a zone of genetic contact and admixture. Molecular variance analysis shows that 94% of genetic variation exists within populations, indicating strong local genetic diversity. Meanwhile, differentiation among countries is low, despite two historical genetic lineages. Pollen remained highly conserved across all populations, suggesting low intraspecific plasticity, while leaf anatomy exhibited phenotypic plasticity. However, these micromorphological variations did not correlate with the two lineages. The results suggest that the genetic structure of C. urucurana is driven by two historical lineages. Brazilian and Paraguayan populations are critical genetic reservoirs and should be prioritized for conservation. The lower variability in Argentina suggests higher vulnerability to environmental shifts. Preserving these lineages is essential for maintaining the species’ evolutionary potential and its pharmacological properties.