| Monochaetum rubescens Gleason, 1938 |
| Monochaetum tenellum Naudin, 1850 |
| Monochaetum triplinerve Naudin, 1845 |
| Mouriri Aubl., 1775 |
| Mouriri exilis Gleason, 1940 |
| Mouriri gleasoniana Standl., 1940 |
| Mouriri muelleri Cogn., 1891 |
| Mouriri myrtilloides (Sw.) Poir., 1824 |
| Mouriri myrtilloides subsp. parvifolia (Benth.) Morley, 1971 |
| Olisbeoideae Burnett, 1835 |
| Oreocosmus Naudin, 1850 |
| Oreocosmus galeottianus Naudin, 1850 |
| Oreocosmus monticola Naudin, 1850 |
| Osbeckia L., 1753 |
| Osbeckia pumila (Bonpl.) DC., 1828 |
| Ossaea DC., 1828 |
| Ossaea ciliata Cogn., 1891 |
| Ossaea disparilis Standl., 1933 |
| Ossaea micrantha (Sw.) Macfad. ex Cogn., 1891 |
| Ossaea trichocalyx Pittier, 1923 |