This study is based on the hypothesis that unmanaged plantations of commercial species do not prevent understory colonization by native species. The research aimed to describe the floristic composition and structure of native arboreal species in the understory of a Corymbia citriodora stand. To this end, 112 plots (10 × 10 m; 1.12 ha) were installed. Six hundred native tree individuals distributed in 54 species, 44 genera, and 20 families were recorded. The regeneration diversity and evenness indices were 3.23 and 0.81, respectively. Native regeneration of C. citriodora understory shows features typical of semideciduous seasonal forests and seems to be at the early stage of regeneration. Results suggest that C. citriodora stands do not prevent understory colonization by native species.