Janssen, Thomas , Schneider, Harald .
Radiations in drynarioid ferns: Evolution of humus collectors as a putative morphological key innovation.
Most species of the palaeotropic fern genera Aglaomorpha and Drynaria, together constituting the monophyletic clade of drynarioid ferns within Polypodiaceae, possess humus-collecting structures as a putative adaptation to their epiphytic habitat. 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 several forms of reduction exist. Additionally, an internal dimorphism between fertile and sterile leaf parts occurs in Aglaomorpha. Despite this complex morphological pattern, evolution of drynarioid morphotypes can be reconstructed postulating a simple sequence of character state changes necessitating only a few elementary processes. We suggest that emergence of humus collectors with subsequent variation on the theme was a key event fostering radiation of the clade. We present a phylogeny of drynarioid ferns based on morphological and molecular (cpDNA) markers. Divergence events are being localized in time and space by the integration of molecular data with fossil and biogeographic evidence. Apart from radiations of Drynaria in Africa and SE Asia, speciation in the diverse Aglaomorpha clade occurs in the Malesian archipelago. The latter event coincides with the collision of the Australian craton with SE Asia in the Upper Miocene. Using lineage per time plots we infer the influence of morphological innovations and geographic events on the radiations of and within drynarioid ferns. Finally, we will discuss approaches that can be used to explore the role of key innovations in the evolution of epiphytic ferns.
1 - University of Goettingen, Department of Systematic Botany, Albrecht von Haller Institute for Plant Sciences, Untere Karspuele 2, Goettingen, D-37073, Germany
2 - Muséum National d'Histoire Naturelle, Systématique et Evolution, USM 0602 Taxonomie et Collections, 16, rue Buffon, Paris, 75005, France
Presentation Type: Paper
Location: Superior B (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 9:45 AM