| Nitzschia inflatula Hasle, 1965 |
| Nitzschia insignis W. Greg., 1857 |
| Nitzschia insignis var. adriatica Grunow |
| Nitzschia insignis var. spathulifera Grunow, 1889 |
| Nitzschia intermedia Hantzsch ex Cleve & Grunow, 1880 |
| Nitzschia interruptestriata Hassall, 1845 |
| Nitzschia kolaczekii Grunow, 1867 |
| Nitzschia kuetzingiana Hilse, 1863 |
| Nitzschia lacunarum Hust., 1930 |
| Nitzschia lacuum Lange-Bert., 1980 |
| Nitzschia laevis Hust., 1939 |
| Nitzschia laevissima Grunow, 1883 |
| Nitzschia lanceolata W. Sm., 1853 |
| Nitzschia lanceolata f. minima Grunow, 1881 |
| Nitzschia leehyi G. Fryxell, 2000 |
| Nitzschia levidensis (W. Sm.) Grunow, 1881 |
| Nitzschia liebetruthii Rabenhorst, 1864 |
| Nitzschia linearis (Agardh) W. Sm., 1853 |
| Nitzschia linearis var. subtilis (Grunow) Hust., 1923 |
| Nitzschia longa Grunow, 1880 |