Anatomical interpretations of the taxonomy of Chamaecrista (L.) Moench sect. Absus (Leguminosae–Caesalpinioideae)

Chamaecrista (L.) Moench (Caesalpinioideae–Leguminosae) with 330 species is organized into six sections: Apoucouita, Absus, Grimaldia, Chamaecrista, Caliciopsis and Xerocalyx. Section Absus is the largest section of the Chamaecrista and is organized into four subsections, viz., subsect. Adenophyllum, subsect. Baseophyllum, subsect. Otophyllum and subsect. Absus. This section is not monophyletic and has a complex taxonomy. This study aims to anatomically characterize 60 taxa of Chamaecrista, identifying meaningful morphoanatomical characters that may shed light on the evaluations of the taxonomic and phylogenetic framework of Chamaecrista, especially C. sect. Absus. Standard light microscopy techniques were used to anatomically characterize the leaves. The anatomical data were subjected to a multivariate analysis (Jaccard index). Epidermal papillae on the abaxial side, the distribution and types of secretory and tector trichomes, variations in the arrangement of the vascular system of the midvein and the type of arrangement of the vascular system of the petiole are useful for separating species or groups of species. The presence and type of secretory structure, the type and position of stomata and the venation pattern are important in establishing the affinities between sections and subsections. The phenetic analysis demonstrates that the anatomical data contribute to the establishment of affinities between sections and subsections, supporting the elevation of the taxonomic status of the clade Baseophyllum to section and the insertion of C. absus (C. sect. Grimaldia) into C. sect. Absus, corroborating molecular studies.