New records, validated name and redefinition in Azolla (Salviniaceae, Pteridophyta) from Costa Rica

In studies of herbarium specimens and living material, we observed that several species in the genus Azolla Lam. are present in different wetlands of Costa Rica, which instigated the search for applicable names of each taxon. According to a morphological and reproductive review, in addition to the species registered and validated, three species were recognized: Azolla filiculoides Lam., A. imbricata (Roxb. ex Griff.) Nakai and A. pinnata R. Br. The first species is the only native species from America, the second is from Asia, and the third is from Africa and Australia. The use of Azolla for fertilizing rice fields and animal feed has led to the introduction of species such as A. imbricata and A. pinnata to countries such as the United States, Colombia, and Ecuador. After their introduction, it is likely that aquatic and migratory birds were responsible for the spread of these species to other countries such as Costa Rica.