In continuation of chemical studies on the genus Senecio focusing on pyrrolizidine alkaloids (PAs), we investigated the alkaloidal composition of four Senecio species: S. polypodioides and S. runcinatus (belonging to section Mulgediifolii) as well as S. madrensis and S. prionopterus (excluded from this section), none of which had been previously studied. The whole plants were extracted with methanol, followed by acidification, reduction with Zn powder, basification, extraction with dichloromethane, and purification via vacuum column chromatography. Isolated alkaloids were identified by spectral comparison with literature data and authentic samples. From S. polypodioides, platyphylline, its hydrochloride, and platyphylline N-oxide were obtained; S. runcinatus yielded rosmarinine and rosmarinine N-oxide; S. madrensis contained platyphylline and senecionine; and S. prionopterus produced senecionine and retrorsine. Chemotaxonomic analysis revealed that both species within section Mulgediifolii and those excluded from it contain 12-membered macrocyclic PAs, though S. prionopterus was found to produce retrorsine—a compound not previously isolated from species in section Mulgediifolii. Further phytochemical research on Senecio species related to section Mulgediifolii is necessary to draw definitive chemotaxonomic conclusions.