Opportunistic diversification has allowed ferns to radiate into epiphytic niches in angiosperm dominated landscapes. However, our understanding of how ecophysiological function allowed establishment in the canopy and the potential transitionary role of the hemi-epiphytic life form remain unclear. Here, we surveyed 39 fern species in Costa Rican tropical forests to explore epiphytic trait divergence in a phylogenetic context. We examined leaf responses to water deficits in terrestrial, hemi-epiphytic, and epiphytic ferns and related these findings to functional traits that regulate leaf water status. Epiphytic ferns had reduced xylem area (-63%), shorter stipe lengths (-56%), thicker laminae (+41%), and reduced stomatal density (-46%) compared to terrestrial ferns. Epiphytic ferns exhibited similar turgor loss points, higher osmotic potential at saturation, and lower tissue capacitance after turgor loss than terrestrial ferns. Overall, hemi-epiphytic ferns exhibited traits that share characteristics of both terrestrial and epiphytic species. Our findings clearly demonstrate the prevalence of water conservatism in both epiphytic and hemi-epiphytic ferns, via selection for anatomical and structural traits that avoid leaf water stress. Even with likely canalized physiological function, adaptations for drought avoidance have allowed epiphytic ferns to successfully endure the stresses of the canopy habitat.

This dataset includes collection of 15 plant functional traits from terrestrial, epiphytic and hemi-epiphytic ferns in Costa Rican tropical forest. Data encompass 29 species, including coverage of eupolypods 1 and 2 clades, from two sites in Costa Rica. Traits include frond morphology, foliar chemistry and leaf water relations via pressume volume curves. Data were collected over multiple fields campaigns in La Selva and Las Cruces Biological Stations. Data include raw data and derived pressure volume traits for all individual ferns for each species. Approximately 6 individual per species, depending on data quality.

See metadata README_fern_water_relations.doc for trait naming conventions (with units and descriptions) for fern_water_relations_master.csv

The authors please request to be notified if the dataset is to be used in publication (Court Campany, courtneycampany@gmail.com). We also request that the users provide the main dataset users (Campany, Pittermann, Watkins) with formal recognition (co-authorship or acknowledgements on publications).