Common Name: Seawracks
Description: Monoecious or dioecious small rhizomatous submerged marine and/or estuarine perennials; rhizome brittle, creeping, with 1 or 2 roots at each node; each node with 2 obovate to ± circular, keeled, translucent scales, the scales placed one above and one beneath the stem; lateral shoots scarcely or not developed, each with 1 pair of leaves, the pair appearing to come directly from the main stem.
Leaves mostly with distinct petiole and lamina.
Flowers unisexual, mostly solitary. Spathe of 2 sessile imbricate keeled bracts. Male flowers pedicellate; perianth segments 3, imbricate; stamens 3, alternating with the segments. Female flowers sessile or almost so; hypanthium long, crowned by 3 reduced perianth segments; styles linear.
Fruit thin-walled, beaked.
Distribution and occurrence: World: c. 10 species, tropical & subtropical regions. Australia: 6 species (native), all States.
Text by S. W. L. Jacobs (1993); edited SWL Jacobs (2007)
Taxon concept:
| | Key to the species | |
| 1 | Erect lateral shoots extremely short, bearing 1 pair of petiolate leaves; flowers mostly on rhizome nodes | 2 |
| Erect lateral shoots elongate, bearing sessile leaves in in 10–20 pairs distichously arranged on each lateral shoot; flowers on erect lateral shoot nodes | Halophila spinulosa |
| 2 | Lateral shoots 0.5–10 mm long, hairy; leaves often with scattered hairs, 10–25 mm long, margins minutely toothed; cross-veins in 6–9 pairs; plants monoecious with 1 male and 1 female flower in each spathe | Halophila decipiens |
| Lateral shoots glabrous, minute or not developed at all; leaves glabrous, 1–7 cm long, margins entire, cross-veins in 10–25 pairs; plants dioecious
Back to 1 | 3 |
| 3 | Styles 6; scales at base of female fertile branch usually green and foliose; leaf blade usually 3–4 times as long as wide | Halophila australis |
| Styles 3; scales all hyaline; leaf blade usually 1.5–2 times as long as wide
Back to 2 | Halophila ovalis |
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