SáNCHEZ-BARACALDO, PATRICIA. Department of Integrative Biology, and University and Jepson Herbaria. University of California, Berkeley, CA 94720. - A recent radiation of Neotropical fern genera in páramo ecosystems.
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