ABSTRACT
The Portuguese and the European Flora refer to the presence of two or three Azolla species in Portugal: A. filiculoides Lam., A. caroliniana Willd. and/or Azolla mexicana Presl., the latter included in the last edition of Flora Europaea. In the present work, the taxonomy of Azolla species is reviewed using the two most important characters that can distinguish between these two/three species: papillae in the dorsal leaf lobe and perine architecture of the megaspore apparatus. Other characteristics, such as the hyaline border cells of the dorsal leaf lobes and the number of glochidia septa in microsporangium massulae, are also used. All the Azolla specimens, collected from several locations in Portugal, were identified as Azolla filiculoides Lam. This identification disagrees with previous published reports on Azolla taxonomy in Portugal as well as with herbarium identification.