论文部分内容阅读
The dwarf dogwoods (subgenus Arctocrania) have been widely known to consist of three circumboreal species Cornus suecica,Cornus canadensis,and Cornus unalaschkensis.A fourth putative species was discovered from the northern Myanmar in 1937,but it had never been formally reported on.Here,we formally report the species on the basis of phylogenetic and morphological evidence and name it Cornus wardiana Rushforth & Wahlsteen (sp.nov.).We conducted phylogenetic and morphometric analyses to determine its evolutionary relationship and differentiation from the existing relatives.We dated the phylogeny using molecular data and conducted a biogeographic analysis to gain insights into the evolution and biogeography of the Arctic-Sino-Himalayan disjunction.The phylogenetic analysis used sequences of the nrlTS and plastid matk and rbcL genes and included all four dwarf dogwoods and 20 other species representing the three other major lineages of Cornus and the outgroup.The morphometric analyses included 60 populations and 102 specimens of dwarf dogwood,representing the entire range of the subgenus.The results showed that C.wardiana diverged first within subgenus Arctocrania in the Miocene,from a wide-spread ancestor.Results from principal component analysis and discriminant analysis also showed that the Myanmar samples are well separated from the others.Taken together,these results suggest that the dwarf dogwood lineage split from the big-bracted dogwoods in Asia or Asia-western North America during the late Paleocene and spread widely to form a Eurasia-North America distribution;the Arctic-Sino-Himalayan disjunction was the result of southward migration in the Miocene followed by extinction in the intervening highland areas.