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Najadaceae


Najas is the only genus in Najadaceae. It is almost cosmopolitan. In Australia, several species of Najas are found in shallow, permanent fresh or brackish water in lakes, estuaries or slow-flowing rivers around the coastal fringe and in central Australia.

Characteristic features of the family Najadaceae in Australia include:

  • leaves whorled, linear, membranous, finely toothed, sheathing the stem at base
  • flowers small, unisexual, axillary, the males comprising a single stamen, the females a single carpel
  • fruit a one-seeded nutlet

Description

Annual or perennial aquatic herbs rooted in the substrate with their leaves submerged. Perennating by rhizomes. Vegetative reproduction absent or by rhizomes or stolons. Stem nodes conspicuously swollen or not. Internal secretions not obvious. Plants glabrous. Leaves distichous or apparently opposite, or in whorls of 35, cauline, sessile. Stipule-like lobes absent. Lamina simple, symmetric, filiform, acicular, subulate, linear or oblong; base lobed or auriculate; margins dentate, serrate or spiny, ±flat; one-veined, with the midrib conspicuous, and the tertiary venation not reticulate; surfaces not punctate; herbaceous, membranous or papery. Leaf ligule absent. Male and female flowers occurring on the same plant or on separate plants. Inflorescences axillary, consisting of solitary flowers. Spathes present or absent. Bracts present or absent. Pollination by water. Flowers stalked. Floral disc absent; nectaries absent. Perianth of 1 whorl only, or vestigial, or absent, with (0) 12 free segments, green or colourless, without contrasting markings, membranous. Fertile stamens 1, or apparently 2 or 4, free of perianth, apparently fused by the anthers, all ±equal. Staminal filament present or apparently absent. Anthers basifixed, not versatile, opening irregularly, 1- or apparently 2- or 4-celled. Ovary superior and sessile. Carpel 1; ovary with 1 locule. Style terminal, single and branched above. Ovule 1, sessile; placentation basal. Fruit a dry indehiscent achene; the perianth on the maturing fruit persistent. Disseminule micro-surface ±smooth or alveolate, yellow, purple or brown, dull. Seeds 1 per fruit. Aril absent. Cotyledons 1. Embryo straight.
(Note: this description has been generated from the coded data compiled for the key. Any errors in the key data will be reflected in the descriptions.)

A treatment of the family Najadaceae has not yet been published in the Flora of Australia. It will appear in Volume 39.

Australian genera of Najadaceae (as recognised for the Flora of Australia)

Najas


Najas (habit)
Photo: S.Jacobs S.Jacobs 


Najas (leafy shoot)
Photo: S.Jacobs S.Jacobs