The Phylogeny And Character Evolution Of Alsineae

Due to the highly homoplastic morphological characters displaying repeated events of reversals and parallelisms,generic delimitation is notoriously difficult in the Alsineae to the degree that the taxonomic study of the group has lagged behind.The range of the tribe still needs to be redefined,and the limit of some heterogeneity genera under the tribe needs to be further divided.Alsineae form a clade of approximately 600 species distributed in the northern hemisphere,which is an ideal model group to study the biological geography and evolution dynamics of diversity in the northern hemisphere.Investigating the phylogeny of Alsineae can not only perfect the classification relationships,but also provide a systematical context to research the origin,distribution and diversity of the tribe,thus contributing to revealing the evolution style of the flora of northern hemisphere.We present a more comprehensive phylogeny of Alsineae based on six chloroplast(matK,rbcL,trnL-F,rps16,psbA-trnH)and nuclear(ITS)loci.Combining the field investigation and specimens identification for the group,the morphological characters of ancestors were reconstructed on the genus level,in order to reveal the variation discipline of morphological characters.The results are outlined as follows:(1)The phylogenetic relationship of Alsineae: The present study reconstructed a more comprehensive phylogeny(13 genera and 118 species and five outgroups)by using the sequence data generated by ourselves or downloaded from the Genbank.The results indicated that the monophyly of Alsineae was strongly supported(BS = 100%,PP = 1.00)and Brachystemma was firstly included in the phylogenetic framework of Alsineae,extending the range of the tribe.The tribe can be divided into two major well-supported sister clade:‘Stellaria+Cerastium clade' and ‘Odontostemma clade',which can be treated as two subtribes of Alsineae.Odontostemma clade comprised the genera Odontostemma,Solitaria,Pseudostellaria,Brachystemma,Lepyrodiclis,and five species of Stellaria(S.americana,S.dichotoma,S.cherleriae,S.dicranoides and S.monosperma).Moenchia,Holosteum and two species of Arenaria were nested within Cerastium and formed a clade nested within Stellaria,which together formed a major clade ‘Stellaria+Cerastium clade' includingMyosoton and Plettkea.(2)Character evolution in Alsineae: Ancestor characters reconstruction was based on the result of BI analysis of total data.Eight key diagnostic morphological characters were chosen to clarify their phologenetic and taxonomic significance.The results showed that absence of petiole,three styles and teeth number of capsule is two times of style were ancestral within Alsineae,which was identical with Stellaria+Cerastium clade.While absence of petiole,pilose pedicel,and teeth number of capsule is two times of style were ancestral within Odontostemma clade.The absence of petiole of Alsineae was lost initially in Brachystemma.The shift from the ancestral of three styles to the derived condition of two styles in Lepyrodiclis and five styles in Myosoton and Cerastium is inferred to have occurred along the branch.The loss of teeth number of capsule is two times of style only once occurred within Lepyrodiclis.(3)Comprehensive analysis from total evidences of phylogeny and ancestor characters states reconstruction: Our analyses strongly confirmed that Alsineae was a monophyletic natural group with high support value.Two evolutionary clades with high support values were distinctly grouped among the tree,supported by morphological characters.We inferred ancestral states for eight taxonomically important morphological characters to clarify their phylogenetic and taxonomic significance.The results showed that absence of petiole,three styles and teeth number of capsule is two times of style were ancestral within Alsineae.These morphological characters are key diagnostic characteristics used as the classification evidences,and especially stellate hair and glandular hairs have important classification value for the definition of infra-genera relationship.