Molecular phylogenetics and biogeography of the mint tribe Elsholtzieae (Nepetoideae, Lamiaceae), with an emphasis on its diversification in East Asia

Pan Li,Ying-Xiong Qiu,Tsung-Hsin Hsieh,Lu-Xian Liu,Tetsuo Ohi-Toma,Cheng-Xin Fu,Joongku Lee,Kenneth M Cameron,Zhe-Chen Qi

doi:10.1038/s41598-017-02157-6

Abstract

Elsholtzia and its allied genera such as Collinsonia and Perilla (tribe Elsholtzieae, Lamiaceae) are an ecologically and economically important plant group consisting of ~71 species, with most species distributed in East and Southeast Asia, and several species in North America. Their phylogeny and historical biogeography resulting in a distant intercontinental disjunction are poorly understood. Here we use two nuclear (ETS, ITS) and five chloroplast (rbcL, matK, trnL-F, ycf1, ycf1-rps15) fragments to reconstruct the phylogeny, biogeographic history, and patterns of diversification of Elsholtzieae. The tribe Elsholtzieae is monophyletic and divided into five clades. The woody Elsholtzia species are nested within herbaceous ones and are inferred to have evolved from herbaceous ancestors. Molecular dating shows that the five major clades were established during the Eocene period, but most of the modern diversity did not originate until the Miocene. The divergence between the New World Collinsonia and the Old World Mosla-Keiskea-Perilla clade was dated to the mid-Miocene. Ancestral area reconstructions suggest that the tribe originated in East Asia, and then dispersed to Southeast Asia and North America. Overall, our findings highlight the important roles of the uplifts of the Qinghai-Tibetan Plateau (QTP) and climate changes from Middle Miocene onwards in promoting species diversification of Elsholtzieae.

Highlights

Among the mint subfamilies, Nepetoideae is the largest, with clearly defined diagnostic morphological characters
The tree topologies from Maximum parsimony (MP), maximum likelihood (ML) and Bayesian analyses are consistent with each other, and the results based on cpDNA data are similar to those based on combined cpDNA + nrDNA data, but with lower support
There were two important dispersals, subsequently, which led to the colonization of Elsholtzieae in the Sino-Japanese subkingdom (D) and Eastern North America (H); the vicariance between zone D and zone H resulted in the divergence between the Mosla-Keiskea-Perilla clade and Collinsonia

Summary

Introduction

Nepetoideae is the largest, with clearly defined diagnostic morphological characters (e.g., hexacolpate and three-nucleate pollen, an investing embryo, presence of rosmarinic acid). The seven genera within Elsholtzieae are widely distributed across East and Southeast Asia, except Collinsonia L., which is a small genus containing four species from eastern North America[14]. The majority of these occur in the mountain ranges of East Asia, centering on the Sino-Himalayan subkingdom (28/43, ~65%, 11 endemics), but extending to the Sino-Japanese subkingdom (20/43, ~47%, 10 endemics) and Southeast/South Asia (18/43, ~42%, 5 endemics), with only one or possibly three species entering the Qinghai-Tibet Plateau, Mongolian Plateau and Central Asia[12, 17,18,19,20,21] This is a diverse genus, and a few Elsholtzia species are characterized by a woody habit (the only ones in the entire tribe that exhibit obvious secondary growth). With increased taxon and character sampling, our paper intends to: (1) test the monophyly of the four non-monotypic genera of the tribe Elsholtzieae; (2) reconstruct the phylogeny and biogeographic history of the tribe and its constituent genera; and (3) examine the patterns of species diversification of the tribe as related to Northern Hemisphere paleoclimate and paleogeography

Methods

Results

Conclusion