Weed Identification

Australia > > Water Lettuce

Water Lettuce

Pistia stratiotes

Family: Araceae.

Form: Water plant

Origin: Native to Asia, Africa, equatorial America and considered native to the Northern Territory. Considered introduced to Queensland, NSW and WA.

Flowers/Seedhead: Small and partly concealed at the base of the plant. Flowers on a column surrounded by a whitish slit funnel-shaped bract (spathe). Female and male flowers separated by a membranous cup that prevents self pollination. The female flower is exposed before the male flowers.

Description: Perennial stoloniferous aquatic herb to 20 cm above water level with feathery roots. Leaves wedge-shaped, pale green, buoyant towards base, to 15 cm long and to 8 cm wide. Fruit a berry, about 6mm wide. Seeds oblong, about 2 mm long.

Distinguishing features: Distinguished by being free-floating with ribbed, spongy, velvety leaves and lettuce-like appearance.

Dispersal: By seed and vegetatively by daughter plants at the end of stolons. Seeds, seedlings and mature plants are moved by water and wind.


Leaves damaged by Neohydronomus
affinus
photo J.R.Hosking

Notes: Reproduces mainly by daughter plants. Under tropical conditions in nutrient rich water, it will produce luxuriant growth, expand rapidly and form obstructive mats. Known to harbour disease-causing mosquitoes. Frost sensitive. Insects, such as the weevil Neohydronomus affinus, have been introduced for biocontrol in Australia.

References:

    Noxious Weeds of Australia. W. Parsons and E. Cuthbertson, 1992, pages 3841. Waterplants of NSW. G. Sainty and S. Jacobs, 1981, pages 6667. Waterplants in Australia. G. Sainty and S. Jacobs, 4th edition, 2003, pages 1011.

Web References: Search Australian web sites for further information on this weed.


Dense feathery roots

Prolific growth (below piggery) Dawson River,
Moura, Qld, May

This weed has been included in the WEEDeck field guide as card W07

More information about WEEDeck is available from Sainty & Associates Pty. Ltd.

 

Australia > > Water Lettuce

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