Home / Anomalous_Items / Aquatic_Macrophytes / Floating_Leaves / Pistia
Click on images for larger format
Name Derivation:
Greek ‘pistos’ = water Common name ‘water lettuce’
Classification:
Pistia Linnaeus Order Alismatales; Family Araceae Monocot, perennial Pistia onsidered to be an evolutionary midpoint along the reduction in flower morphology between terrestrial ancestors and the highly reduced flowers of Spirodela, Lemna, and ultimately Wolffia (Arber 1919, Sculthorpe 1967).
Morphology:
Floating plant forms a rosette of thick leaves with parallel ‘veins’ (vascular bundles) and entire margins; each leaf can be up to 14 cm long. Trichomes covering the leaf epidermis aid buoyancy by trapping bubbles. Feathery roots are suspended underneath the water surface. Monoecious. Flowers inconspicuous (a few mm tall), male and female flowers located close together with spadix partly fused with spathe, one female flower below and a few male flowers above (Cook et al. 1974), growing near the center of the leaf rosette. Asexual reproduction occurs by budding in a ‘lateral pocket derived partly from the leaf sheath and partly from axil tissue, comparable with the vegetative pocket of Lemna and Spirodela (Sculthorpe 1967). Daughter plants remain attached to the parent plant with a short stolons that eventually may abscise.
Habitat:
Freshwater. Widely distributed globally in tropical and subtropical waterways. Excess growth in eutrophic waters can eliminate aquatic plants with submerged foliage, and cause fish kills by causing anoxia under dense mats of Pistia that block gas exchange with the atmosphere. Mechanical harvesting and removal of Pistia biomass onto land is useful in ‘phytoremediation’ of excess phosphorus and nitrogen in waterways. Spread of Pistia and other aquatic plants into SE Asia as fodder for pigs is undoubtedly due to its harvest as a fodder for pigs and to a lesser extent cattle (Sculthorpe 1967). Spread into other regions often follows intentional introduction into aquaria and ‘water gardens (Ibid.).
References:
Arber, A. 1919. On the vegetative morphology of Pistia and the Lemnaceae. Proc. R. Soc. ser. B, 91:96-103. Cook, C.D.K, B.J. Gut, E.M. Rix, J. Schneller, and M. Seitz 1974. Water Plants of the World. Dr. W. Junk b.v.,Publishers. The Hague (561 pp). Sculthorpe, C.D. 1967. The Biology of Aquatic Vascular Plants. Edward Arnold (Publishers) Ltd., London (610 pp).