2013 Volume 64 Issue 3 Pages 159-177
This paper reviews studies of the phylogeny and evolution of epiphytism in ferns, with an emphasis on Davalliaceae. The family forms the largest, generally epiphytic monophyletic clade with Polypodiaceae including grammitids. Several other lineages include epiphytes. Molecular phylogenies suggest that the davallioid-polypodioid epiphytes diverged from the secondary hemi-epiphytic Oleandraceae in angiosperm-dominated forests in the Paleogene. The evolution of epiphytism in vittarioids and lycophytic Huperzia may be derived directly from terrestrial ancestors. The stepwise evolution of epiphytes is characterized by the ecological shift of gametophytes from the ground to trees following sporophytes, while the abrupt evolution involves the simultaneous shift. Furthermore, reversals from epiphytes to secondary hemi-epiphytes or to terrestrial plants are also likely in other ferns. Precise identification of life forms in the field offers a sound basis of research on epiphyte evolution. There are several morphological traits correlated with life-form change (e.g., rhizome length and dorsiventrality; absorbing or adhering roots; peltate, stalked, dense scales), as well as physiological traits. Epiphytic gametophytes are strap-shaped, ribbon-like or filamentous, branched, gemmiferous and long-lived in, e.g., grammitids, Hymenophyllaceae and vittarioids, while, like terrestrial gametophytes, they are heart-shaped and monocarpic in, e.g., Davalliaceae and Polypodiaceae. Comparative eco-physiological research of gametophytes is needed to investigate the transitions from terrestrial to epiphytic gametophytes. Interactions between epiphytes and hosts should be clarified to understand the evolution of epiphytism. Mildly hemiparasitic epiphytes, e.g., Pyrrosia piloselloides (Polypodiaceae), probably obtain water and nutrition from their hosts and may represent a further step in the evolutionary sequence.
