Morphology
The leaves of H.decipiens occur in pairs and consist of a distinct blade and petiole. The leaf blades are typically narrower and approximately 1.0-2.5 cm in length. The leaf blade is hairy and translucent with prominent marginal and mid veins, the mid vein being most conspicuous. There are 6-9 pairs of cross veins. The margin of the leaf blade is finely serrated along its length; this feature is best observed with a hand lens or low power microscope. The rhizome scales are hairy. Halophila decipiens often has a 'dirty' appearance due to sediment entangled in the hairs of the leaves.

Diagnostic features
Translucent, hairy, oval leaves with serrated margin. Prominent venation. Hairy rhizome scales.

Likely to be confused with
Other Halophila species, particularly H.ovalis and H.ovata.
The leaves of H.decipiens are generally three times longer than broad, whereas the leaves of H.ovalis and H.ovata are less elongate, i.e. up to 2.5 times longer than broad. A more obvious feature is the margin of the leaf blade, which is smooth in H.ovalis and H.ovata, but finely serrate in H.decipiens.