Key to species of Sphacelaria
| 1 | Arms of modified lateral branches (propagula) cylindrical, like a broad V | S. rigidula |
| 1 | Arms of propagula not cylindrical, approximately triangular or club-like in outline | 2 |
| 2 | Propagula club-like, top rounded or thickened | S. novaehollandiae |
| 2 | Propagula triangular, like a top; plant tufts dense and nearly black | S. tribuloides |