| Senecio albonervius Greenm., 1914 |
| Senecio alienus B.L. Rob. & Seaton, 1893 |
| Senecio alvarezensis Greenm., 1912 |
| Senecio ammophilus Greene, 1885 |
| Senecio amplifolius (DC.) Sch. Bip., 1845 |
| Senecio ampullaceus Hook., 1836 |
| Senecio anacletus Greene, 1901 |
| Senecio andrieuxii DC., 1838 |
| Senecio angulifolius DC., 1837 |
| Senecio angulifolius var. ingens Greenm., 1914 |
| Senecio anisophyllus Klatt, 1888 |
| Senecio aphanactis Greene, 1888 |
| Senecio arborescens Steetz, 1854 |
| Senecio argutus Kunth, 1820 |
| Senecio aschenbornianus Schauer, 1847 |
| Senecio axillaris Klatt, 1882 |
| Senecio barba-johannis DC., 1837 |
| Senecio barkleyi B.L. Turner, 1985 |
| Senecio bartlettii Greenm., 1950 |
| Senecio bellidifolius Kunth, 1820 |