Novas perspectivas do valor taxonômico de Cipselas de Dendrophorbium (Cuatrec.) C. Jeffrey e Senecio L. (Senecioneae - Asteraceae)

Abstract

Studies have shown the importance of anatomy for the classification and understanding of the evolution of cypselae in Asteraceae, the largest plant family. However, some of their tribes have been poorly studied and have unclear taxonomy and evolutionary patterns. The Senecioneae tribe is the largest tribe within Asteraceae and has major taxonomic controversies in its infratribal classifications. Two genera of this tribe, Dendrophorbium and Senecio, have great affinity with each other, and some researchers say that these genera should be merged. Thus, an anatomical study with seven species of Dendrophorbium and one of Senecio was made in order to seek important information that can help in the resolution of problems regarding the classification of Dendrophorbium and the arrangement of Senecioneae. The fruits of the species were submitted to the usual anatomy techniques and the images were obtained by engaging a camera to a light microscope. The cypselae did not present a defined cross-section shape. Senecio adamantinus is the only species to have twin hairs in its exocarp. Species of Dendrophorbium, except D. catharinensis and D. paranense, presented secretory ducts in the mesocarp, an unprecedented feature for Senecioneae. The mesocarp of the analyzed species presented a high taxonomic value, since the number of vascular bundles, the number of secretory ducts and the presence of lignified cells on this region can vary among the species. Dendrophorbium brachycodon, D. catharinensis, D. glaziovii, D. paranense and S. adamantinus have no lignified cells on the mesocarp, while all the other species analyzed have. Secretory ducts occur in varying numbers among species, and generally are associated with vascular bundles. The present study demonstrates that, despite having similarities with Senecio, Dendrophorbium has its own characteristics, a fact that suggest its delimitation as a proper genus. It was also concluded that an anatomical approach is important for species identification, which can bring a new perspective on the evolution of mesocarp within the tribe, as well as its classification.