Phylogeny And Biogeography Of The Genus Hedysarum L. (Fabaceae)

The legume family(Fabaceae)is the third largest flowering plant family with about 19,500 species in about 751 genera.The family exhibits a high level of species diversity and evolutionary success in various ecosystems worldwide.The genus Hedysarum L.(Fabaceae: Hedysareae)consists of about 160 species of perennial herbs to rarely shrublets.It mainly distributes in temperate Eurasia,with a few species in North Africa and North America.Previous phylogenetic studies of the genus Hedysarum showed that the nuclear and the plastid topologies might be incongruent,and the systematic position of the Hedysarum sect.Stracheya clade was uncertain.This dissertation studied the phylogeny and biogeography of the genus Hedysarum.The main findings were as follows.(1)Phylogenetic relationships of Hedysarum were investigated based on the nuclear ITS,ETS,PGDH,SQD1,TRPT and the plastid psbA-trnH,trnC-petN,trnL-trnF,trnS-trnG,petN-psbM sequences.Both nuclear and plastid data support two major lineages in Hedysarum: the Hedysarum s.s.clade and the Sartoria clade.In the nuclear tree,Hedysarum is biphyletic with the Hedysarum s.s.clade sister to the Corethrodendron + Eversmannia + Greuteria + Onobrychis clade(the CEGO clade),whereas the Sartoria clade is sister to the genus Taverniera DC.In the plastid tree,Hedysarum is monophyletic and sister to Taverniera.The incongruent position of the Hedysarum s.s.clade between the nuclear and plastid trees may be best explained by a chloroplast capture hypothesis via introgression.The Hedysarum sect.Stracheya clade is resolved as sister to the H.sect.Hedysarum clade in both nuclear and plastid trees,and these analyses support merging Stracheya into Hedysarum.Based on the new evidence from multiple sequences,Hedysarum is not monophyletic,and its generic delimitation needs to be reconsidered.Hedysarum should be split into two genera: Hedysarum s.s.and Sartoria,rendering each one monophyletic.(2)By using the nuclear ETS and ITS sequences,as well as the plastid psbA-trnH,trnC-petN,trnL-trnF and trnS-trnG sequences,the phylogeny,divergence time and ancestral distribution of the genus Hedysarum s.s.were investigated.The results showed various topological incongruences between the nuclear and the plastid trees,indicating multiple hybridization\introgression events in the evolutionary history of this group.Hedysarum s.s.originated in early Miocene,in relation with a rapid uplift phase of the Qinghai-Tibetan Plateau.The ancestral distribution of Hedysarum s.s.was reconstructed as West Asia and Mediterranean + Pan-Himalayas,then a vicariance took place,leading Hedysarum s.s.with a Pan-Himalayas distribution.Various vicariance and dispersal events were indicated,and members of Hedysarum s.s.may migrate to Central Asia and East Asia several times through the “Central Asiatic Highland Corridor” and “Chinese Southwest-Northeast Corridor”,respectively.In Quaternary,H.ussuriense may migrate to Japan from China mainland through the land bridge connecting them in glacial periods.Members of Hedysarum s.s may migrate to North America through the Bering Land Bridge,but vicariance took place in Quaternary,leading to the intercontinental disjunction of this group.The phylogenetic results also showed that the species rank of each of H.chinense,H.smithianum,H.prezewalskii,H.americanum shoud be accepted,and the taxonomical states of some taxa still need more investigations.(3)A new species,Hedysarum cuonanum(Fabaceae,Hedysareae),was described from the eastern Himalaya in China.This new species is similar to H.xizangense,but differs by its lanceolate or narrowly elliptic leaflet blade,ovate or lanceolate bracteole about half the length of calyx tube,acute or obtuse standard apex,and mucronate keel apex.It also resembles H.longigynophorum,but can be distinguished by its leaflet blade with 13–19 secondary veins on each side,abaxial calyx tooth about 1.5 times as long as the adaxial teeth,standard as long as keel,and elliptic or ovate loment article.Phylogenetic analyses based on the nuclear ITS,ETS sequences,and the plastid psbA-trnH,trnC-petN,pet N-psbM sequences showed that H.cuonanum is sister to H.xizangense,and the H.cuonanum + H.xizangense clade is then sister to H.longigynophorum.