Exploring the evolution of humus collecting leaves in drynarioid ferns (Polypodiaceae, Polypodiidae) based on phylogenetic evidence

Abstract

Most species of the paleotropic fern genera Aglaomorpha and Drynaria, together constituting a monophyletic clade (drynarioid ferns), possess humus-collecting structures as an adaptation to their epiphytic life form. Humus-collectors are either present as a specialized foliar structure (external leaf dimorphism) or as a specialized leaf part (internal dimorphism). Apart from these basic patterns there are several forms of reduction and an internal fertile - sterile dimorphism in Aglaomorpha. We present a phylogeny of drynarioid ferns based on morphological and molecular (cpDNA) markers. The genus Aglaomorpha was found to be monophyletic, whereas Drynaria is likely to be a paraphyletic assemblage including a grade of Himalayan to Southern Chinese taxa basal to Aglaomorpha. The evolution of humus-collectors is reconstructed by plotting their character state changes onto the obtained phylogeny. Despite the complex morphological pattern across species, evolution of drynarioid humus-collecting structures can be reconstructed postulating a simple sequence of character state changes based on only a few elementary processes. © Springer-Verlag 2005.