WATER LETTUCE

Pistia stratiotes

Arum Family [Araceae]

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flower
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24th Sept 2014, Leeds & L/pool Canal, Maghull, Merseyside. Photo: © RWD
These are growing as garden pond throwouts, in the same stretch of canal your Author also found Water Hyacinth another garden pond throw out. Water Lettuce is not hardy enough to overwinter in the present climate of the UK, and will die out over winter, so does not appear in Stace III. It was first discovered in Africa near Lake Victoria.


24th Sept 2014, Leeds & L/pool Canal, Maghull, Merseyside. Photo: © RWD
These are quite small rosettes of floating leaves; in warmer countries they can get to 60cm across and will completely cover a lake or pond as a mat, blocking gas exchange with the water thereby killing fish. They also block the light killing any other submerged plants. The sheer weight of large specimens can also crush other aquatic plant species. In smaller ponds it never gets so massive, and in the UK will die out overwinter in outdoor ponds.


24th Sept 2014, Leeds & L/pool Canal, Maghull, Merseyside. Photo: © RWD
Being a member of the Arum family Araceae, which usually have a long prominent spathe, this plant has very tiny flowers with a tiny greyish white spathe with two compartments, a larger compartment for the male anthers and a smaller compartment for the female style, with a gap in the compartment containing the style.


24th Sept 2014, Leeds & L/pool Canal, Maghull, Merseyside. Photo: © RWD
Your Author thinks that the grayish object in the centre is the double compartmented spathe. The male and female parts are not to be seen in this photo. There is a really great photo on another website showing both style with discoidal stigma and stamen with anthers in a cog-type radial arrangement at the  Botany Department, University of Hawaii, Manoa which I hope they don't mind me linking to here.


24th Sept 2014, Leeds & L/pool Canal, Maghull, Merseyside. Photo: © RWD
The hairs on the underside of the leaves are longer than those on upper leaf surfaces, perhaps to make it float better(?)


Not to be semantically confused with : Lettuce [a vegetable with similar name]

It cannot over-winter in the UK which is too cold for it.

The flower is tiny, less than 1cm long. The flower is contained within a figure-of-8 spathe; the larger compartment encompassing the 5 or more short radial yellowish anthers, the smaller compartment (and the one with a gap in) the off-white stigma with spherical style atop. Don't forget that this plant is an Arum, which have spathes, although in the case of Water Lettuce, the spathe is minute and in the centre of the rings of leaves.


  Pistia stratiotes  ⇐ Global Aspect ⇒ Araceae  

Distribution
 family8Arum family8Araceae

 BSBI maps
genus8Pistia
Pistia
(Water Lettuce)

WATER LETTUCE

Pistia stratiotes

Arum Family [Araceae]