| Xanthocoma Kunth, 1818 |
| Xanthocoma humilis Kunth, 1820 |
| Xerochrysum Tzvelev, 1990 |
| Xerochrysum bracteatum (Vent.) Tzvelev, 1990 |
| Xerotium Bluff & Fingerh., 1825 |
| Ximenesia Cav., 1794 |
| Ximenesia cordata Kunth, 1820 |
| Ximenesia encelioides Cav., 1794 |
| Ximenesia encelioides var. nana A. Gray, 1853 |
| Ximenesia exauriculata (B.L. Rob. & Greenm.) Rydb., 1906 |
| Ximenesia foetida (Cav.) Spreng., 1826 |
| Ximenesia hispida Kunth, 1820 |
| Ximenesia microptera DC., 1836 |
| Xylorhiza Nutt., 1841 |
| Xylorhiza frutescens (S. Watson) Greene, 1896 |
| Xylorhiza orcuttii (Vasey & Rose) Greene, 1896 |
| Xylorhiza wrightii (A. Gray) Greene, 1896 |
| Xylothamia G.L. Nesom, 1990 |
| Xylothamia diffusa (Benth.) G.L. Nesom, 1990 |
| Xylothamia johnstonii G.L. Nesom, 1990 |