A Phylogenetic Study On Hedysareae Sensu Lock(Leguminosae)

The tribes Hedysareae sensu Lock belong to subfamily Papilionoideae of Leguminosae(Fabaceae), including Alhagi, Calophaca, Caragana, Corethrodendron, Ebenus, Eversmannia,Halimodendron, Hedysarum, Onobrychis, Sartoria, Sulla and Taverniera, with a distributionin northern Eurasia, North Africa and North America. Taxa of this tribe can be used as fodder,ornamental and erosion control plants. Through phytotaxonomic history, various taxonomiststreated Hedysareae sensu Lock and closely related taxa differently, and its monophyly remainunclear up to date. As plant molecular systematics becomes more and more popular andmature, using such method to explore the phylogenetic relationship and revise existingtaxonomic system are valid and viable. Present study sampled 198 accessions(represented187 species) of Hedysareae sensu Lock and closely related groups, collected from Eurasia, N.Africa and N. America. Based on the nuclear ITS and plastid mat K, trn L-F and psb A-trn Hmarkers, using methods of Maximum Parsimony(MP), Maximum Likelihood(ML) andBayesian Inference(BI), with taking morphological, biogeographic and habitat informationinto consideration, phylogenetic analyses and taxonomic revision are conducted. The mainresults and conclusions are described as below.1. Hedysareae sensu Lock is not monophyletic, and its relationships with tribe Galegeaeare unclear. Galegeae is polyphyletic. Hedysareae sensu Lock includes two strongly supportedclades: the Caraganean clade and the Hedysaroid clade. Results herein support treating theHedysaroid clade as tribe Hedysareae, comprising nine genera: Alhagi, Corethrodendron,Ebenus, Eversmannia, Greuteria, Hedysarum, Onobrychis, Sulla and Taverniera. Eight ofthem can be supported as monophyletic genera, except for Eversmannia. Hedysarum asdelimited here consists of three main clades: the first clade corresponds to H. sect. Hedysarum;the second clade contains the re-circumscribed H. sect. Multicaulia, consisting of the group offormer H. sect. Multicaulia plus former monotypic genus Sartoria; and the third clade is equalto the re-delimitated H. sect. Stracheya, including H. tibeticum and two species previouslyplaced in H. sect. Multicaulia(H. kumaonense and H. lehmannianum). These three sectionslargely correspond to mesic, xeric and psychrophilic group, possibly implying a key impact ofhabitat changes on the diversification of Hedysarum.2. The results verify the monophyly of Caraganeae but re-circumscribed based on theCaraganean clade, including Calophaca, Caragana and Halimodendron, with Calophacabeing well-supported. Halimodendron nests in a paraphyletic Caragana, within which threemonophyletic sections are recognized: C. sect. Bracteolatae, C. sect. Caragana and C. sect.Frutescentes. A new tribe, Chesneyeae, is established on the basis of the Chesneyean clade,containing Chesneya, Gueldenstaedtia and Tibetia. Within Chesneyeae, Chesniella andSpongiocarpella are re-merged in Chesneya; on the other hand, Gueldenstaedtia and Tibetiaretain their generic status. Genera in Chesneyeae display a vicarious distribution andspeciation of Chesneya seems partly attribute to habitat variation.