Key to the species of Rhizoclonium
| 1 | Cells mostly 200 - 400 µm diam.; rhizoidal branchlets frequent, non-septate or divided into 3 - 4 short cells | R. grande |
| 1 | Cells less than 100 µm diam | 2 |
| 2 | Plants in large mats or skeins, on mud or free-floating; rhizoidal branches few or lacking; filaments often less than 50 µm wide | R. riparium |
| 2 | Plants variable in appearance and habitat; rhizoidal branchlets usually present, some rebranched; filaments often 50 - 100 µm wide | R. africanum |