Application of floral microcharacters to solving taxonomic problems in Argentinean species of the genus Senecio (Asteraceae, Senecioneae)

Senecio L., the largest genus in the tribe Senecioneae (Asteraceae), contains a significant number of taxonomic difficulties, given that its boundaries are not clearly defined and species identification is sometimes complicated. A study was carried out to evaluate the importance of micromorphological characters in the resolution of such taxonomic problems. The study included 18 South American taxa from series Xerosenecio, Corymbosi and Otoperi. The characters studied include the stigmatic surface and apices of the stylar branches, the filament collar, base and appendages of the anthers, and the pollen shape, size, sculpture and aperture. The microcharacters of the stamens (filaments and anthers) and the presence of margo in the pollen provide taxonomically useful traits for the differentiation of related taxa and infraspecific entities in the genus Senecio. The mesoaperture in the pollen grain in eight Argentinean taxa of Senecio is recorded for the first time. Finally, unique floral microcharacters (sagittate anther base) and palynological features (cavea not evident, long spines) in S. otites were observed.