The pteridophyte Azolla filiculoides Lam. and the monocotyledoneous Heteranthera limosa (Sw.) Willd, have been found in the ricefields of Northem Aragón (Spain) widening the infesting weed catalogue. They are provided data for the identification of these kinds, current state on the distribution areas and their behavior. Finally a new locality of Heteranthera reniformis Ruiz y Pavón is presented.