Description: Submerged monoecious or dioecious, much-branched, diffuse submerged aquatic annuals or perennials.
Leaves opposite or whorled, with a sheathing base and toothed margins; sheaths open, often auriculate.
Flowers small, unisexual, axillary, 1–few together. Male flowers spatheate, with 1 stamen enclosed in a thin 2-lobed envelope, envelope ruptured as peduncle lengthens at anthesis; anther 1- or 4-sporangiate. Female flowers with or without a spathe; ovary solitary, carpel 1, 1-locular; stigmas 2–4.
Fruit a capsule with a thin pericarp; seed 1, with pits in regular or irregular rows.
Distribution and occurrence: World: c. 32 species, cosmopolitan. Australia: 8 species (native), all mainland States.
Text by S. W. L. Jacobs
Taxon concept:
| | Key to the species | |
| 1 | Leaves c. 5 mm wide with inauriculate sheathing bases and numerous spine-tipped teeth along the margins; female flower mostly with 3 stigmas | Najas marina |
| Leaves 1–3 mm wide with auriculate sheathing bases, and several inconspicuous teeth along the margins; female flower with 2- or 3-lobed stigmas | 2 |
| 2 | Leaf auricles obtuse, 0.3–0.5 mm long; seed less than 1.7 mm long | Najas browniana |
| Leaf auricles acuminate, 0.5–1.5 mm long; seed 1.7 mm or longer
Back to 1 | Najas tenuifolia |
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