Colloquia

         Neotropical Pteridology: A Dedication to Robbin Moran

New records of hemiepiphytes in ferns and their implications for the evolution of epiphytism

Presenting Author
David Barrington
Description
Robbin Moran has a knack for making field observations that have led to major insights in the evolution of ferns. One of these has been documenting the existence of hemiepiphytes in ferns, a growth habit previously overlooked in the group.  Collaborating with students in his OTS field courses, Robbin published observations of hemiepiphytism in Elaphoglossum amygdalifolium and Vandenboschia collariata. These studies stimulated the further discovery of hemiepiphytism in other species belonging to Hymenasplenium, Dendroconche, Campyloneurum, Pleopeltis, and Leptochilus. Field observations also led to a paper examining growth habit in Polybotrya, which was determined to be a root-climber. Robbin incorporated growth habit into phylogenetic reconstructions of the Dryopteridaceae to test whether hemiepiphytes were an intermediate step the evolution of holo-epiphytism from the terrestrial ancestors. The reconstructions, however, were limited by the few examples of fern hemiepiphytes known at the time.  Inspired by Robbin’s research, we set out to observe and document more examples of hemiepiphytes in ferns. Here we present new records of fern hemiepiphytes from the American tropics and Papua New Guinea. We document hemiepiphytism for the first time in Asplenium, Crepidomanes, Lindsaea, and Sphaerostephanos, and for the second time in Leptochilus. We find that despite evolving in many unrelated lineages, hemiepiphytic ferns converge on similar morphological adaptations to this habit. Ecologically, they seem to be most prevalent in mid- to low-elevation tropical humid forests. We find no evidence that they were an intermediate step in the evolution of holo-epiphytism, instead nearly every case appears to be a reversion away from holo-epiphytism.