| Sidneya pinnatilobata var. megaphylla (Butterw. ex B.L. Turner) E.E. Schill. & Panero, 2011 |
| Sidneya tenuifolia (A. Gray) E.E. Schill. & Panero, 2011 |
| Sigesbeckia L., 1753 |
| Sigesbeckia agrestis Poepp. & Endl., 1843 |
| Sigesbeckia andersoniae B.L. Turner, 1978 |
| Sigesbeckia blakei (McVaugh & Lask.) B.L. Turner, 1978 |
| Sigesbeckia cordifolia Kunth, 1818 |
| Sigesbeckia hartmannii B.L. Turner, 1978 |
| Sigesbeckia jorullensis Kunth, 1818 |
| Sigesbeckia orientalis L., 1753 |
| Sigesbeckia pringlei D.L. Schulz, 1988 |
| Sigesbeckia repens B.L. Rob. & Greenm., 1895 |
| Silphium L., 1753 |
| Silphium arborescens Mill., 1768 |
| Silphium trilobatum L., 1759 |
| Silybum Adans.,1763 |
| Silybum marianum (L.) Gaertn., 1791 |
| Simsia Pers., 1807 |
| Simsia adenophora (Greenm.) S.F. Blake, 1913 |
| Simsia amplexicaulis (Cav.) Pers., 1807 |