Taxonomic delimitation in Aspidosperma sect. Pungentia (Apocynaceae) based on morphological and leaf anatomical traits

Aspidosperma is one of the most representative genera in Apocynaceae in Brazil, composed of trees or small trees popularly known as perobas. The genus is distributed throughout tropical America, from Mexico to Argentina, with the exception of Chile. It comprises 80 species, 42 of which occur in Brazil, which is the center of diversity for the genus. Aspidosperma triternatum and Aspidosperma quebracho-blanco, name the Aspidosperma sect. Pungentia, section is easily distinguished from the others, even in the vegetative state, by grouping species that have leaves with pungent apexes, unique in the genus. However, A. triternatum and A. quebracho-blanco are difficult to distinguish due to the morphological similarities they present, such as the pungent apex of their whorled leaves and the yellowish white color of their flowers. Therefore, our objective was to develop a study to obtain leaf morphological using the usual methods of microscopy. The most important diagnostic characters useful for delimiting the species were: the number of pairs of secondary veins; the patterns of distance between these and the median and distal region, as well as the reticulation of these veins; the branching of the tertiary veins; the impression of the quaternary veins as well as their development and the shape of the areola; shape of epidermal cells; cuticular ornamentation pattern; types and distribution of trichomes; distribution of stomata; organization and number of cell layers in mesophyll. We have shown from the performed study that the species have remarkable morphological and anatomical differences which made possible a better circumscription of the group.