Morphology
Fine, rather delicate seagrasses, Halodule species possess a thin, herbaceous rhizome system with a short erect shoot at each node, and fine thin roots. The leaf sheath is well developed and remains in place long after the blade has been shed. The leaf blade is linear and flat. It always has three veins, the midvein being the most conspicuous - a good distinguishing character of this genus. A ligule is present. Phenotypic variation is quite high, particularly in H.uninervis and the leaves may be of variable width (falling between 0.25 and 5.00 mm), and of variable length, commonly 5 cm or longer. Species are usually distinguished on the basis of leaf tip morphology and to a lesser extent, leaf width. As there is some overlap with respect to leaf widths of the two species, this is often a poor character to use when dividing Halodule into its constituent species. In rare instances, leaf tip morphology may also be unreliable and in such cases it is safer to consign specimens to generic level only. Likewise, if leaf tips are unavailable, e.g. in dugong or turtle digesta samples, it is often impossible to key seagrass fragments out to a species level.

Diagnostic features
Thin, herbaceous rhizome, often with numerous leaf scars. Thin linear leaf blades with three longitudinal veins.