Systematics and evolution of lycophytes and ferns
Welcome to this special issue of the Journal of Systematics and Evolution focused on the systematics and evolution of lycophytes and ferns. It is our hope that it will inspire innovative research on these plants at this critical time where human activities are transforming biodiversity as we know it. Lycophytes and ferns are distinct evolutionary lineages, with ferns strongly supported as sister to seed plants and lycophytes, in turn, sister to this large (euphyllophyte) clade. Notably, however, lycophytes and ferns do share many features, including vascular plant apomorphies (e.g. vascular tissue) and land plant plesiomorphies (e.g. spore dispersal and the absence of seeds) For these reasons, they have long been collectively treated as "pteridophytes" and it still seems appropriate to address the biology of both lineages together. This special issue was initiated in the context of the most recent international scientific meeting dedicated to ferns and lycophytes, Next Generation Pteridology, which was organized by Eric Schuettpelz and colleagues in 2015. Although it is not designed as the proceedings of that meeting, the theme of "next generation" is maintained by including a diverse array of early career contributors (along with those who are well established) and by focusing on a selection of topics for which data are coming from novel sources enabling innovative research. These topics may challenge long held hypotheses or support emerging new hypotheses. Of course, this special issue cannot cover all aspects of lycophyte and fern biology, and recent more comprehensive compilations already exist (e.g. Ranker Haufler, 2008; Mehltreter et al. 2010) Here, we aim to give attention to contributions that will hopefully be relevant to the research of the future generations of pteridologists. Topics were selected to cover a wide range of issues, including some that may, at first blush, appear a bit old fashioned. At the same time, some readers may be surprised by the absence of contributions in some frequently highlighted fields, but some outstanding reviews have already been published in areas such lycophyte and fern genomics (e.g. Sessa Der, 2016) All contributions to this special issue share a common theme of aiming to document and understand lycophyte and fern diversity. Such documentation arguably requires the ability to classify theseplants andweare pleased to publish here thefirst installation of a new approach to the classification of lycophytes and ferns from the Pteridophyte Phylogeny Group (PPG I, 2016) The initiative towards the establishment of the Pteridophyte Phylogeny Group was inspired, but not constrained, by the successesof theAngiospermPhylogenyGroup. It involved an open call to anyone working on the systematics of lycophytes and ferns, with the aim to establish a communitybased classification. The result required considerable compromise and is quite distinct from existing classifications. Diversity is also the focus of a critical review of our current understanding of fern and lycophyte systematics in the Neotropics (Almeida Salino, 2016) Although this region hasbeen intensively studied bymany prominent pteridologists, including John Mickel, Robbin Moran, Alan Smith, and Rolla Tryon, major gaps in our knowledge remain (e.g. undersampled regions and lineages requiring taxonomic revisions) This review also highlights the need to study these ferns within a broader framework (i.e. beyond national floras) A similar message is given in another contribution, which explores the distinct pteridophyte flora of the East African Biodiversity Hotspot (Liu et al. 2016) This latter study was enabled by the outstanding contributions of many pteridologists who explored Africa, culminating in the work by Jacobous "Koos" Roux (2009) and further emphasizes the need to identify and address gaps in our knowledge concerning the distribution and taxonomy of pteridophytes, in both species rich and speciespoor regions. Interestingly, these two contributions to this special issue also serve to collectively highlight an interesting shift in the study of tropical floras away from the historical powerhouses of botany based in North America and Europe. Links between evolutionary and ecological processes are at the core of the research on elevational diversity patterns summarized by Kessler et al. (2016) This study provides an outstanding example of the power that can be achieved by integrating observations of local diversity gradients into a global hypothesis. A somewhat more local perspective is provided by focusing on the pteridophyte diversity of Hawai'i (Ranker, 2016) Oceanic islands are known to have exceptionally high proportions of pteridophyte diversity (Kreft et al. 2010) but are also widely recognized as "evolutionary laboratories" in which to explore the accumulation of biodiversity. The Hawai'ian islands are unique in combining geographic isolation with extensive habitats that are suitable for ferns and lycophytes. Future studies may attempt to compare this oceanic archipelago with other islands that are rich in pteridophyte diversity, such as the Mascarene Islands (Hennequinet al. 2014) and toemploypteridophytediversity as an indicator for the impactof climatechangeon thebiodiversity on oceanic islands with high elevations (Pouteau et al. 2016) Two contributors to this special issue were willing to assemble perspectives on topics closely associated with a pair of the most influential pteridologists of the mid 20 century: Irene Manton and Edward Klekowski. The two reviews explore state of the art of research on hybridization (Sigel, 2016) and apomictic reproduction (Grusz, 2016) Both reviews comprehensively summarize our current understanding and point out promising research directions that take advantage of new genomic tools (the access to genomic data has historically been one of the main limitations of research on these topics) Progress in our understanding of these aspects of pteridophyte biology has always been closely linked to the establishment of new methods, as well as the careful application of groundbreaking concepts (Haufler, 2014) JSE Journal of Systematics and Evolution