Key to the common species of Laurencia
| 1 | Plants without lenticular thickenings in medulla | 2 |
| 1 | Plants with lenticular thickenings in medulla, with non-projecting tangential walls of cortical cells | L. nidifica J Agardh |
| 2 | Tangential walls of cortical cells projecting | 3 |
| 2 | Tangential walls of cortical cells non-projecting | 4 |
| 3 | Plants compressed to flattened | L. dotyi Saito |
| 3 | Plants not compressed or flattened, with final branchlets radially arranged in small branched clusters | L. majuscula (Harvey) Lucas |
| 4 | Plants green except for basalmost part which may be reddish | L. mcdermidiae Abbott |
| 4 | Plants not green | 5 |
| 5 | Plants with axes describing arches, ultimate branchlets irregularly attached, often unilateral; plants dark brown with gold-colored branchlets | L. yamadana Howe |
| 5 | Plants without arching branches, stiffly radially branched to 2-3 orders, the ultimate branchlets firm and unbending | L. cartilaginea Yamada |
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