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Morphology:

'Floating leaf' aquatic macrophytes are defined here as having the majority of photosynthetic leaves resting (floating) on the surface tension of the water.  Their buoyancy is assured either by inflated stems or leaf petioles (Eichornia is an extreme case of inflated petioles), or by hydrophobic trichomes on the leaf surfaces.  Submerged stems connect to rhizomes or roots. 

Some plants are freely floating over the water surface and generally have feathery accessory roots with a high surface area to volume ratio.  Others are anchored in substrate and thus are limited in their maximum depth.  The roots are subject to low dissolved oxygen concentration so must be tolerant to that condition.

Habitat:

References: