How Epiphytic Are Filmy Ferns? A Semi-Quantitative Approach

Abstract

Similar to plants in many other families, members of the Hymenophyllaceae use numerous substrates for growth, e.g., soil, rocks or tree bark. However, substrate preference does not only differ among species but can also vary among members of the same species. There have been several attempts in the past to appropriately capture this variation, but none proved feasible or was replicated in any subsequent work. In our approach, we use textual information from numerous sources like checklists, floras and species descriptions to come up with a quantitative index of the preference of 450 species of filmy ferns (=c. 75% of all species of the family) for epiphytic, lithophytic or terrestrial growth. We show that the majority of species have clear habitat preferences, while strict habitat specificity is rather uncommon. Our compilation will be an important input for future ecological and phylogenetic studies in this family, but the presented approach is of much more general interest: it is immediately applicable to other taxonomic groups and should eventually allow us to replace the current approach of assigning species to distinct categories (epiphyte, lithophyte or terrestrial) by one that finally reflects biological variability more appropriately.