Aerenchyma is widely known to be lysigenous, schizogenous or, more recently, expansigenous. The interpretation and understanding of its function is questionable, given the lack of extensive knowledge on the development and cellular changes of this tissue. The aerenchyma of Pistia stratiotes L. roots reportedly originates from packet lysigeny. However, our observations suggest schizogenous development. Our objective was to analyse the aerenchyma ontogeny of P. stratiotes roots and evaluate the cell wall morphological and chemical changes during the formation of the aerenchyma. Aerenchymatous inner cortex of schizogenous origin was observed under light and electron microscopy. The lacunae are formed by the separation, division and stretching of the cells, which remain alive until maturity. Analyses using monoclonal anti-glycan antibodies show that formation of that type of aerenchyma apparently proceeds through the same mechanisms as the genesis of intercellular spaces. However, the greatest changes occur when cells undergo stretching, including the loss of methyl-esterification and detection of arabinans, which are not directly involved in cell separation. Thus, other factors may account for the formation of schizogenous aerenchyma. New insights into the primary cell wall in Araceae are also discussed.