There are two traditionally recognized fern genera in the Neotropics that together form a monophyletic group, Jamesonia and Eriosorus. Molecular phylogenetic studies suggest that neither genus is a natural group and that several lineages with "jamesonia" morphology have undergone a fairly recent radiation, approximately 3-5 million years ago, in páramo ecosystems. "Jamesonia" is unique among the ferns in its highly modified vegetative and ecological characteristics. Some of the most outstanding morphological features of this genus are: 1) indeterminate growth, 2) xeromorphic and coriaceous leaves, and 3) extremely reduced pinnae. A robust phylogeny was generated based on sequence data of the External Transcribed Spacer (ETS) and the Internal Transcribed Spacers (ITS) of 18s-26S rDNA, and the plastid coding region and spacer of the rps4 gene. Several conclusions can be made about the evolutionary history and biogeographic patterns of the eriosorus-jamesonia complex such as: 1) “jamesonia” was found to be polyphyletic, having arisen independently at least three times, 2) two well supported clades can be recognized, roughly corresponding to the Northern vs. Southern Andes, and 3) the sister taxon of the Andean radiation was found to be in Brazil, Eriosorus myriophyllus. Character evolution studies indicate a sharp ecological shift in the evolution of "jamesonia’s" ecological preferences. In addition, there is a repetitive trend towards pinnae reduction and indeterminate growth, perhaps correlated with the extreme environmental factors prevailing in Neotropical páramo ecosystems. The independent lineages of "jamesonia" provide the first examples of recent adaptive radiations in the ferns.

Key words: adaptive radiation, ETS, ITS, Neotropical ferns, páramo, rps4