river lettucen.rare an aquatic plant, Pistia stratiotes (family Araceae), common in tropical rivers and streams; the water lettuce.
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1897 M. KingsleyTrav. W. Afr. 378 Great floating masses of river lettuce (Pistia stratiotes).
1920 A. ArberWater Plants xvii. 213 In Africa, the River Lettuce, Pistia Stratiotes, plays a similar part to the Water Hyacinth of America in hindering navigation.