Towards resolving the complete fern tree of life.

Samuli Lehtonen,Dirk Steinke

doi:10.1371/journal.pone.0024851

Abstract

In the past two decades, molecular systematic studies have revolutionized our understanding of the evolutionary history of ferns. The availability of large molecular data sets together with efficient computer algorithms, now enables us to reconstruct evolutionary histories with previously unseen completeness. Here, the most comprehensive fern phylogeny to date, representing over one-fifth of the extant global fern diversity, is inferred based on four plastid genes. Parsimony and maximum-likelihood analyses provided a mostly congruent results and in general supported the prevailing view on the higher-level fern systematics. At a deep phylogenetic level, the position of horsetails depended on the optimality criteria chosen, with horsetails positioned as the sister group either of Marattiopsida-Polypodiopsida clade or of the Polypodiopsida. The analyses demonstrate the power of using a ‘supermatrix’ approach to resolve large-scale phylogenies and reveal questionable taxonomies. These results provide a valuable background for future research on fern systematics, ecology, biogeography and other evolutionary studies.

Highlights

Ferns comprise ca. 12,000 extant species [2] and are the closest living relatives of the seed plants [1]
The first molecular systematic studies on ferns were published in the mid 1990s [3,4,5], and set the direction for modern fern systematics
Well-sampled analyses are crucial for understanding the lower level phylogenetic patterns, but due to their generally limited scope the higher level relationships remain untested

Summary

Introduction

Ferns (monilophytes sensu Pryer et al [1]) comprise ca. 12,000 extant species [2] and are the closest living relatives of the seed plants [1]. Numerous molecular phylogenetic studies have either focused on certain classically defined fern groups by sampling members from the group studied, or tested the backbone fern classification by sampling exemplar species of higher taxa. Both kinds of studies have, specific limitations to recover the complete fern tree of life. Well-sampled analyses are crucial for understanding the lower level phylogenetic patterns, but due to their generally limited scope the higher level relationships remain untested. The relationships between higher taxonomic ranks (such as genera or families) may be seriously obscured if only one or few representatives of each group are sampled [6,7]

Methods

Results

Conclusion