| Levringia Kylin, 1940 |
| Levringia brasiliensis (Mont.) A.B. Joly, 1953 |
| Melanosiphon Wynne, 1969 |
| Melanosiphon intestinalis (D.A. Saunders) Wynne, 1969 |
| Meneghiniella Setch. & N.L. Gardner, 1924 |
| Meneghiniella brandegeei Setch. & N.L. Gardner, 1924 |
| Mesogloia C. Agardh, 1817 |
| Mesogloia andersonii Farlow, 1889 |
| Myelophycus Kjellm., 1893 |
| Myelophycus intestinalis D.A. Saunders, 1901 |
| Myriactula Kuntze, 1898 |
| Myriactula johnstonii (Setch. & N.L. Gardner) Feldmann, 1945 |
| Myriactula marchantiae (Setch. & N.L. Gardner) Feldmann, 1945 |
| Myrionema Grev., 1827 |
| Myrionema clavata Harv., 1833 |
| Myrionema expansum J. Agardh, 1847 |
| Myrionema strangulans Greville, 1827 |
| Myriotrichia Harv., 1834 |
| Myriotrichia subcorymbosa (Holden) H.L. Blomq., 1958 |
| Nemacystus Derbès & Solier, 1850 |