Molecular phylogeny of Galium L. of the tribe Rubieae (Rubiaceae) – Emphasis on Chinese species and recognition of a new genus Pseudogalium

摘要

GaliumL. is the largest genus in the tribe Rubieae, with about 667 species distributed worldwide. Previous researches mainly focused on species from the Americas and Europe. In the present paper, we greatly increased the number of samples examined from eastern Asia (especially China), representing the most comprehensive sampling ofGaliumto date. A total of 194 species and variations (subspecies) ofGaliumwere sampled to determine phylogenetic relationships, using two nuclear and five chloroplast markers. Our data are largely consistent with all previous phylogenetic results and confirmed thatGaliumis non-monophyletic, as are most of its sections. Most members ofGalium, including the Chinese taxa, fall into three large clades mixed with other genera from theGaliums.l. group; the exception being the distinctGalium paradoxumMaxim., the first diverged lineage in theGaliums.l. group, which was treated as a new genus (PseudogaliumL.-E. Yang, Z.-L. Nie & H. Sun, gen. nov.). TheGaliums.s is a well-supported clade comprised entirely ofGaliumspecies, usually with six or more leaves per whorl, mostly from the Old World. Samples fromG. maximowiczii(Kom.) Pobed,G.sect.Depauperataand sect.Aparinoides, together with a few fromAsperulasect.GlabellaandMicrophysa(Schrenk ex Fisch. & C.A. Mey.) Pobed., form the second clade. The third clade comprises taxa purely fromGaliumthat usually have four leaves per whorl, from both the New and Old World. Our results also indicated that the monotypic genusMicrophysashould be retained and clarified phylogenetic relationships of some specific confused taxa from China. Unlike prior inferences, the combination of opposite leaves associated with two stipules is proposed as the ancestral characteristic of theGaliums.l. group and even the tribe. In addition, the shapes of different corolla and inflorescence types are important for distinguishing some taxa within Rubieae.