Key to the species of Caulerpa
| 1 | Erect axes and primary branches with serrate margins, simple without branchlets | C. serrulata |
| 1 | Erect axes and primary branches with numerous branchlets, often regularly arranged and with distinctive shapes, rebranched in some species | 2 |
| 2 | Branchlets with narrow stalks and broad, flared or spherical tips | 3 |
| 2 | Branchlets cylindrical, flat and curved, tapering toward tip | 4 |
| 3 | Branchlet tips globose, with constriction between inflated tip and supporting "stalk" | C. lentillifera |
| 3 | Branchlet tips of various shape, without conspicuous constrictions between apex and "stalk" | C. racemosa |
| 4 | Branchlets terete, evenly arranged and continuous along erect axes and primary branches | C. sertularioides |
| 4 | Branchlets distinctly pointed at tip, compressed, or terete with successive dichotomies | 5 |
| 5 | Branchlets flattened, sickle-shaped (curved with pointed apices) , not rebranched | C. taxifolia |
| 5 | Branchlets terete, arranged in whorls (rarely distichous) and rebranched dichotomously several times | 6 |
| 6 | Branchlets opposite (paired) or in distinct symmetrical whorls of 4 (5), uniformly broad (about ¼ to 1/3 branch diameter) for about half the length of branchlet, then successively forked with branchlets from each dichotomy narrower and tapering to tip; plants to 2 cm | C. webbiana |
| 6 | Branchlets 2 to several, uniformly slender, in verticillate clusters along axes and branches with dimensions of successive dichotomies similar throughout; plants to 3 - 7 cm tall | C. verticillata |