Key to the species of Enteromorpha
| 1 | Plants branched throughout, either with repeated branching and rebranching, or with profuse proliferations (mostly uniseriate of various lengths) | 2 |
| 1 | Plants seemingly unbranched, others branched primarily or only near the base | 4 |
| 2 | Plants typically to 4 cm high, ultimate branchlets numerous, uniseriate; cells cuboidal to rectangular | E. paradoxa |
| 2 | Plants 5 to 40 cm high; if present, branchlets usually multiseriate | 3 |
| 3 | Cells of European specimens described as large, often to 45 - 50 µm; chloroplast occupying only part of cell with numerous pyrenoids | E. clathrata |
| 3 | Cells of European specimens described as small, often 6 - 18 µm diam.; chloroplast occupying most of cell with single large pyrenoid | E. prolifera |
| 4 | In surface view, cells mostly or in some areas arranged in longitudinal row ( in narrow tubes sometimes in both longitudinal and transverse directions | E. flexuosa |
| 4 | In surface view, cells typically not in rows but arranged irregularly throughout; plants often inflated tubes of different widths | 5 |
| 5 | Upper parts of plant above stipitate base flat with cell layers united (not hollow), or remaining free along entire or a portion of margin | E. linza |
| 5 | Plant with no stipe, or insignificant stipe; tube not united anywhere; tubular throughout | E. intestinalis |