| Oryzopsis erecta Beal, 1896 |
| Oryzopsis fimbriata (Kunth) Hemsl., 1885 |
| Oryzopsis florulenta Pilg., 1899 |
| Oryzopsis fournieriana Hemsl., 1885 |
| Oryzopsis grisebachii Speg., 1901 |
| Oryzopsis hymenoides (Roem. & Schult.) Ricker ex Piper, 1906 |
| Oryzopsis membranacea (Pursh) Vasey, 1891 |
| Oryzopsis pringlei Beal, 1890 |
| Oryzopsis seleri Pilg., 1909 |
| Oryzopsis stipoides (Trin. & Rupr.) Speg., 1901 |
| Oryzopsis uruguayensis (Griseb.) Speg., 1901 |
| Osterdamia Neck. ex Kuntze, 1891 |
| Osterdamia matrella (L.) Kuntze, 1891 |
| Osterdamia zoysia Honda, 1922 |
| Osterdamia zoysia var. tenuifolia (Thiele) Honda, 1922 |
| Osterdamia zoysia var. typica Honda, 1922 |
| Otachyriinae Butzin, 1970 |
| Otatea (McClure & E.W. Sm.) C.E. Calderón & Soderstr., 1980 |
| Otatea acuminata (Munro) C.E. Calderón & Soderstr., 1980 |
| Otatea acuminata subsp. acuminata (Munro) C.E. Calderón & Soderstr., 1980 |