Morphology
Halophila ovalis could be described as a delicate 'cloverlike' seqagrass. Leaves have petioles, occur in pairs and can be morphologically very variable, with leaf blades oval to elliptical in shape, and ranging from 1-4 cm in length; the leaf blade is 0.5-2.0 cm wide. Leaves have 10 - 25 pairs of crossveins ascending at 45-60 degrees to the mid vein. Intramarginal veins are present and the leaf margin is smooth, and although the leaves often appear to arise directly off thr rhizome, there is in fact a very short lateral shoot enclosed in two membranous scales. Fine roots originate at the base of each shoot.

Diagnostic features
Oval-elliptical leaf blade on petiole. 10-25 pairs of cross veins.

Likely to be confused with

Halophila ovata
Generally, the leaves of H.ovalis are more elongate/elliptical (approximately 2.0-2.5 times longer than broad) than the smaller, more oval leaves of H.ovata (approximately 1-2 times longer than broad). These species also differ in the number and angle of cross veins relative to the mid vein. Various authors have questioned the legitimacy of separating H.ovata and H.ovalis. Although these species are typically distinguished on the basis of leaf length and width, ranges of leaf lengths and widths can show quite a degree of overlap, and it is therefore often difficult to classify intermediate forms. Similarly, the number of cross veins is variable. For these reasons, many workers tend to group these two forms together under the species H.ovalis, or classify to generic level only.

Halophila decipiens
The leaf of H.ovalis is readily distinguishable from H.decipiens by its smooth or entire margin, compared to the finely serrated margin of H.decipiens, and perhaps less reliably, on the basis of the length to width ratio. H.ovalis leaves are 2.0-2.5 times longer than broad, compared to the leaves of H.decipiens which are 2.75-3.25 times longer than broad. In addition, the leaf blade of H.decipiens is hairy rather than smooth, and the marginal and mid veins are prominent compared with H.ovalis.