title: Does the Arcto-Tertiary biogeographic hypothesis explain the disjunct distribution of Northern Hemisphere herbaceous plants? The case of Meehania (Lamiaceae).
abstract: Despite considerable progress, many details regarding the evolution of the Arcto-Tertiary flora, including the timing, direction, and relative importance of migration routes in the evolution of woody and herbaceous taxa of the Northern Hemisphere, remain poorly understood. Meehania (Lamiaceae) comprises seven species and five subspecies of annual or perennial herbs, and is one of the few Lamiaceae genera known to have an exclusively disjunct distribution between eastern Asia and eastern North America. We analyzed the phylogeny and biogeographical history of Meehania to explore how the Arcto-Tertiary biogeographic hypothesis and two possible migration routes explain the disjunct distribution of Northern Hemisphere herbaceous plants. Parsimony and Bayesian inference were used for phylogenetic analyses based on five plastid sequences (rbcL, rps16, rpl32-trnH, psbA-trnH, and trnL-F) and two nuclear (ITS and ETS) gene regions. Divergence times and biogeographic inferences were performed using Bayesian methods as implemented in BEAST and S-DIVA, respectively. Analyses including 11 of the 12 known Meehania taxa revealed incongruence between the chloroplast and nuclear trees, particularly in the positions of Glechoma and Meehania cordata, possibly indicating allopolyploidy with chloroplast capture in the late Miocene. Based on nrDNA, Meehania is monophyletic, and the North American species M. cordata is sister to a clade containing the eastern Asian species. The divergence time between the North American M. cordata and the eastern Asian species occurred about 9.81 Mya according to the Bayesian relaxed clock methods applied to the combined nuclear data. Biogeographic analyses suggest a primary role of the Arcto-Tertiary flora in the study taxa distribution, with a northeast Asian origin of Meehania. Our results suggest an Arcto-Tertiary origin of Meehania, with its present distribution most probably being a result of vicariance and southward migrations of populations during climatic oscillations in the middle Miocene with subsequent migration into eastern North America via the Bering land bridge in the late Miocene.
authors: School of Life Science, Yunnan University, Kunming, Yunnan, China; Key Laboratory for Plant Diversity and Biogeography of East Asia, Chinese Academy of Sciences, Kunming, Yunnan, China; University of Chinese Academy of Sciences, Beijing, China.
authors: Tao
authors: T
authors: Deng
authors: Key Laboratory of Plant Resources Conservation and Utilization, College of Biology and Environmental Sciences, Jishou University, Jishou, Hunan, China.
authors: Ze-Long
authors: ZL
authors: Nie
authors: Department of Biology, University of Nebraska at Kearney, Kearney, Nebraska, United States of America.
authors: Bryan T
authors: BT
authors: Drew
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Chinese Academy of Sciences, Kunming, Yunnan, China.
authors: Sergei
authors: S
authors: Volis
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Chinese Academy of Sciences, Kunming, Yunnan, China.
authors: Changkyun
authors: C
authors: Kim
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Chinese Academy of Sciences, Kunming, Yunnan, China.
authors: Chun-Lei
authors: CL
authors: Xiang
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Chinese Academy of Sciences, Kunming, Yunnan, China.
authors: Jian-Wen
authors: JW
authors: Zhang
authors: School of Life Science, Yunnan University, Kunming, Yunnan, China.
authors: Yue-Hua
authors: YH
authors: Wang
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Chinese Academy of Sciences, Kunming, Yunnan, China.
authors: Hang
authors: H
authors: Sun
mesh_terms: D001483:Base Sequence; D001499:Bayes Theorem; D018744:DNA, Plant / Q000378:metabolism; D019686:Lamiaceae / Q000145:classification* / Q000235:genetics; D010802:Phylogeny; D018087:Plastids / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant