Argentina is located in the southern part of South America, with climates ranging from warm, temperate to cold, and encompassing several wetlands and a variety of freshwater bodies such as lakes, reservoirs, ponds, rivers and shallow lakes, where phytoplankton may develop. A remarkably large number of taxa have been reported in taxonomic monographs, inventories of regional floras, and floristic lists in ecological papers. Several planktonic algae have a wide geographical distribution and can be found in other parts of the world with similar environmental conditions. Other habitats, particularly those in warm and circumpolar regions, harbour species and infraspecific entities with a limited geographical distribution. On the other hand, some taxa have been recorded only in this country and are thus considered endemic. Taxonomic studies of different groups, mainly Chlorococcales, Desmidiaceae, Euglenophyceae and Diatomophyceae, have revealed several species and infraspecific taxa new to science. The present article provides an overall picture of phytoplankton diversity in the different regions of Argentina.