Key to species of Feldmannia
| 1 | Plants with extensive matted rhizoidal systems endophytic among utricles of Codium species; spindle -shaped plurilocular structures near basal portion of plants | F. elachistaeformis |
| 1 | Plants with a small number of rhizoids; endo/epiphytic on a wide variety of hosts; plurilocular structures cylindrical, distributed throughout plants below meristematic regions | F. indica |