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Plantwise Technical Factsheet

water lettuce (Pistia stratiotes)

Description

P. stratiotes is a free-floating, stoloniferous plant with sessile leaves in rosettes. Leaves pale-green, up to 20 cm long and 10 cm wide, mostly spathulate to broadly obovate with a rounded to truncate apex, with  7-15 prominent veins radiating fanwise from the base; both surfaces , in particular the lower surface, covered by a dense mat of white woolly hairs (Cook et al., 1974; Aston, 1977; Holm et al., 1977; Sainty and Jacobs, 1981). Inflorescence axillary, solitary, ascending; spathe 1.3-1.5 cm long, convolute and adnate to the spadix below, spreading above, whitish; spadix with a single pistillate flower at base, and with 2-8 staminate flowers above, shorter than the spathe. Flowers unisexual, the perianth wanting; stamens 2; ovary 1-locular, with numerous ovules, the style slender, the stigma penicillate. Fruit thin-walled, many-seeded. Seeds cylindrical, rugulose. (Acevedo-Rodríguez and Nicolson, 2005)

The morphology of Pistia varies largely owing to the influence of environmental factors. In a survey of two populations in ponds of distinct hydrochemical characteristics, two biotypes were identified that propagate true. The biotypes were distinct regarding biomass, productivity allocation, pH of the cell saps, chlorophyll, nucleic acids, total free amino acid content of the leaves and total nitrogen, crude protein and phosphorus in whole plants (Rao and Reddy, 1984). The leaves rise into the air, but under conditions less favourable for optimal growth they may lie flat on the water.

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