A new approach to an old problem – how to categorize the habit of ferns and lycophytes
Gerhard Zotz, Lisa Armenia, Helena J R Einzmann- Plant Science
Abstract
Background and Aims
Substrate preferences are often treated as species traits and are used to distinguish different habits, i.e. an epiphytic, lithophytic or terrestrial habit. Such a categorization ignores, however, substantial intraspecific variation. An approach that takes biological variability within a species into account is needed.
Methods
We focused on four large genera of ferns and lycophytes, and found relevant information in more than 500 sources such as online data bases, checklists, floras and species descriptions. Translating textual information into a quantitative index, we quantified the propensity to grow on either substrate as a continuous trait for 1475 species.
Key Results
Only a minority of species exhibited strict substrate fidelity, but a majority of them show clear habitat preferences. The relative frequencies of intermediates between strict lithophytes, epiphytes, and terrestrials does not support the frequent notion of ecological similarity of the lithophytic and epiphytic habitat.
Conclusions
The compiled data are immediately useful for ecological and evolutionary studies with the focal taxa. More importantly, we propose to replace the concept of distinct habits with one of gradual differences. This should have a profound impact on any such study with plants in general.