Key to the common species of Griffithsia
| 1 | Plants consisting of beadlike cells 0.5 to 1.5 mm in diam | 2 |
| 1 | Plants consisting of elongate cells less than 500 µm in diam | 3 |
| 2 | Cells more than 1 mm in diam., only basal most cells of filament oval to obovate | G. metcalfii Tseng |
| 2 | Cells less than 1 mm in diam., lower cells of filament often cylindrical and elongate | G. heteromorpha Kützing |
| 3 | Filaments di,tri,poly-chotomously branched above, reproductive structures terminating shortened lateral branches, involucrate | G. subcylindrica Okamura |
| 3 | Filaments irregularly branched, usually unbranched near summit; reproductive structures borne between upper vegetative cells | G. schousboei Montagne |
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