Americabaetis (Insecta: Ephemeroptera: Baetidae), previously considered synonymous with Acerpenna, is reinstated and given generic rank. The genus differs from Acerpenna in lacking hindwings, gills on abdominal segment 1, and a conical process between the male genital forceps, and in possessing apically rounded gills on abdominal segment 7. The genus has a general Neotropical distribution with a northern limit in east-central Mexico. Five new species of Americabaetis are described from South America: A. alphus, new species, from Argentina, Bolivia, Brazil, Chile, and Paraguay; A. labiosus, new species, from Brazil, Paraguay, and Uruguay; A. longetron, new species, from Brazil, Paraguay, and Uruguay; A. maxifolium, new species, from Paraguay; and A. titthion, new species, from Brazil. Americabaetis boriquensis, new combination; A. intermedius, new combination; A. naranjoi, new combination; A. pleturus, new combination; and A. robacki, new combination, are reviewed.