SUMMARY The fern genus Actiniopteris is studied from the taxonomical point of view. It is regarded by some authors as a «genus incertae sedis». It belongs to the order of the Pteridales. A comparison with other genera of this order has shown that it is nearer to the Cryptogrammaeeae than to any other family. However, its distinctive features are so important as to justify its classification as a new independent family which is described under the name of ACTI- NIOPTERIDACEAE. Two species were originally assigned to Actiniopteris: A. radiata and A. australis. The former is selected as type of the genus. In modern times Actiniopteris has been regarded as monotypic, but a study of more than 500 specimens has shown that five species may be kept distinct. Two of them are those originally referred to the genus by LINK. Three are described as new species. Thus the genus is regarded as consisting of A. radiata, A. di- morpha, A. pauciloba, A. semiflabellata and A. australis. The differences between them are based...