Phylogenetic And Biogeographic Studies Of Theaceceae With A Special Referece To Stewartia

Theaceae is included in order Ericales by Angiosperm Phylogeny Group (APG). It comprises of nine genera, over460species. Several phylogenetic studies of Theaceae have been published in recent years based on morphological and molecular data. Three major lineages or tribes have been recognized including Stewartieae (Stewartia and Hartia), Gordonieae (Gordonia, Franklinia, and Schima), and Theeae (Camellia, Laplacea, Apterosperma, Polyspora, and Pyrenaria). In this study we used ca.40,000base pairs of chloroplast genes to gain a better understanding of the phylogeneics and biogeography of Theaceae. Stewartia is disjuncted distribution in eastern Asia and eastern North America (EA-ENA). It has two species in southeastern United States and the remaining species in eastern Asia. we used ITS, trnL-F and psbA-trnH sequences to reveal the relationship between Hartia and Stewartia. Combination with the geographic, paleoclimatic, fossil evidences, we studied the implication of biogeography pattern of EA-ENA. There are four main conclusions of our research:1) Evolution of morphological characteristics of Theaceae and its classification systemOur broad sampling of Theaceae as well as other major lineages of the Ericales provides strong support for the monophyly of Theaceae excluding Ternstroemiaceae (Pentaphyllaceae in APG2009). Our sequence data from the chloroplast genome further support the three clades of Theaceae. The first-diverging position is Stewartieae. Theeae and Gordonieae are closer related to each other.The trace of evolution of morphological characteristics in Theaceae is endosperm may have evolved from copious layers in Stewartieae, thin layers in Gordonieae, to total absence in Theeae. The number of capsule valves decreased from5in Stewartieae and Gordonieae to3in Theeae. Carpels may have evolved from free in Stewartieae, basally connate in Gordonieae to well developed central columnella in Theeae. Perforation bars in vessel have probably evolved in the direction of reduction from Stewartieae to Gordonieae and Theeae.In habit character, the deciduousness has evolved at least twice in Theaceae. The deciduousness in Franklinia is a specialized feature in the tribe due to global temperature has decreased from the Mid-Miocene. Therefore, adaptation to increasingly cold climate might be associated with the transformation of leaf habit from evergreen to deciduous in the ancestral population of Franklinia. In contrast, Hartia diverged from deciduous lineages of Stewartia becoming evergreen at ca.14.99mya, when evergreen monsoon forests may have taken shape in Southeast Asia.2) Phylogenetic relationship of Gordonieae.There are three genera of Gordonieae:Schima, Franklinia and Gordonia. Generic relationships of Gordonieae have not been fully resolved by previous molecular studies. Our chloroplast data show strong support for the early divergence of Gordonia (ca.14mya) in Gordonieae and for the sister relationship of Franklinia and Schima. Comparing to Gordonia, Franklinia and Schima share more similar morphological characters in fruit and seed.3) Phylogenetic relationship of Stewartieae.The North American species Stewartia ovata is more closely related to Asian species of Stewartia than to the other North American species S. malacodendron. Species of Hartia form a strongly supported monophyletic clade, which is sister to the branch containing S. ovata and Asian species of Stewartia. Therefore, the Hartia clade is embedded within Stewartia in the phylogenetic trees. There're no significant morphological differences between two genera except the leave habit and the numbers of buds scales. Our data support the combination of Hartia and Stewartia. Combining molecular data (ITS, trnL-F and psbA-trnH) and morphological characters, a new classification of Stewartia is proposed. Three new combinations and four new synonmy are included. Furthermore, the genus Stewartia is divided into three sections because of the color of anthers and habits.4) Biogeography and distribution patternThe three tribes of Theaceae are all disjuncted distributed between eastern Asia and America. Gordonieae and Stewartieae show disjuncted distribution between eastern Asia (EA) and North America (NA). Franklinia and Gordonia are monotypic, North American taxa. Schima has a wide distribution in subtropical and tropical areas of southern Asia. In Stewartieae, Species of evergreen species (Hartia) occur in central and southern China, whereas deciduous species (Stewartia) have two species in southeastern United States and the remaining species in eastern Asia. Divergence times of eastern Asian-eastern North American disjunct taxa:Franklinia and Schima in Gordonieae is ca.11.32million years ago (mya), from North America to Asia through the Bering land bridge; the two divergence time between S. malacodendron to all other Stewartia species and Stewartia ovata to Asian deciduous species are ca.14.99mya and ca.7.8mya, respectively. The estimated time is from the Mid-Miocene to late Miocene, which agrees with recent estimates of the disjunction in other angiosperm taxa.There are about half of evergreen species of Stewartia distributed in Guangdong and Guangxi province. And two thirds of deciduous species distributed in the region of eastern China and Japanese archipelago before it's formatted. Those regions are/or used be the diversity centers of evergreen and deciduous species of Stewartia, respectively.