Phylogeny, Taxonomy, and Biogeography of Pterocarya (Juglandaceae).

Yann Fragnière,Hitoshi Sakio,Hong-Hu Meng,Bin-Jie Ge,Sébastien Bétrisey,Gregor Kozlowski,Yi-Gang Song,Hamed Yousefzadeh,Ying Li

doi:10.3390/plants9111524

Abstract

Relict species play an important role in understanding the biogeography of intercontinental disjunctions. Pterocarya (a relict genus) is the valuable model taxon for studying the biogeography of East Asian versus southern European/West Asian disjunct patterns. This disjunction has not been as well studied as others (e.g., between Eastern Asia and North America). Several phylogenetic studies on Pterocarya have been conducted, but none have provided a satisfactory phylogenetic resolution. Here, we report the first well-resolved phylogeny of Pterocarya using restriction site-associated DNA sequencing data based on the sampling of all taxa across the entire distribution area of the genus. Taxonomic treatments were also clarified by combining morphological traits. Furthermore, fossil-calibrated phylogeny was used to explore the biogeography of Pterocarya. Our results support the existence of two sections in Pterocarya, which is in accordance with morphological taxonomy. Section Platyptera comprises three species: P. rhoifolia, P. macroptera, and P. delavayi. Section Pterocarya also comprises three species: P. fraxinifolia, P. hupehensis, and P. stenoptera. The divergence between the two sections took place during the early Miocene (20.5 Ma). The formation of the Gobi Desert and climate cooling of northern Siberia in the Middle Miocene (15.7 Ma) might have caused the split of the continuous distribution of this genus and the formation of the East Asian versus southern European/West Asian disjunct pattern. Lastly, the divergence between P. hupehensis and P. stenoptera as well as between P. rhoifolia and P. macroptera/P. delavayi (10.0 Ma) supports the late Miocene diversification hypothesis in East Asia.

Highlights

Understanding geographic patterns of species diversity is one of the central aims of biogeography [1,2,3]
There is a group of genera (e.g., Acer, Aesculus, Forsythia, Liquidambar, Picea, Parrotia, Pterocarya, and Zelkova) sharing the East Asian versus southern European/West Asian disjunct pattern, including those in North America [19,20,21,22]
All these studies ignore the biogeography of East Asia versus southern European/West Asian disjunct patterns

Summary

Introduction

Understanding geographic patterns of species diversity is one of the central aims of biogeography [1,2,3]. There is a group of genera (e.g., Acer, Aesculus, Forsythia, Liquidambar, Picea, Parrotia, Pterocarya, and Zelkova) sharing the East Asian versus southern European/West Asian disjunct pattern, including those in North America [19,20,21,22]. All these studies ignore the biogeography of East Asia versus southern European/West Asian disjunct patterns. The Sino-Japanese Floristic Region (SJFR) in East Asia harbors the most diverse temperate flora worldwide and is the most important glacial refugium for Cenozoic relict flora [23]. Many of the previous phylogeographic studies in the SJFR focused on individual regions, such as the Sino-Himalayan Forest [24,25,26] and the Sino-Japanese

Methods

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Discussion

Conclusion