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

Galium L. 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 of Galium to date. A total of 194 species and variations (subspecies) of Galium were sampled to determine phylogenetic relationships, using two nuclear and five chloroplast markers. Our data are largely consistent with all previous phylogenetic results and confirmed that Galium is non-monophyletic, as are most of its sections. Most members of Galium, including the Chinese taxa, fall into three large clades mixed with other genera from the Galium s.l. group; the exception being the distinct Galium paradoxum Maxim., the first diverged lineage in the Galium s.l. group, which was treated as a new genus (Pseudogalium L.-E. Yang, Z.-L. Nie & H. Sun, gen. nov.). The Galium s.s is a well-supported clade comprised entirely of Galium species, usually with six or more leaves per whorl, mostly from the Old World. Samples from G. maximowiczii (Kom.) Pobed, G. sect. Depauperata and sect. Aparinoides, together with a few from Asperula sect. Glabella and Microphysa (Schrenk ex Fisch. & C.A. Mey.) Pobed., form the second clade. The third clade comprises taxa purely from Galium that usually have four leaves per whorl, from both the New and Old World. Our results also indicated that the monotypic genus Microphysa should 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 the Galium s.l. group and even the tribe. In addition, the shapes of different corolla and inflorescence types are important for distinguishing some taxa within Rubieae.

The origin of unique diversity in deglaciated areas: traces of Pleistocene processes in north-European endemics from the Galium pusillum polyploid complex (Rubiaceae).

The role of glacial oscillations in shaping plant diversity has been only rarely addressed in endemics of formerly glaciated areas. The Galium pusillum group represents a rare example of an ecologically diverse and ploidy-variable species complex that exhibits substantial diversity in deglaciated northern Europe. Using AFLP and plastid and nuclear DNA sequences of 67 populations from northern, central, and western Europe with known ecological preferences, we elucidate the evolutionary history of lineages restricted to deglaciated areas and identify the eco-geographic partitioning of their genetic variation. We reveal three distinct endemic northern lineages: (i) diploids from southern Sweden + the British Isles, (ii) tetraploids from southern Scandinavia and the British Isles that show signs of ancient hybridization between the first lineage and populations from unglaciated central Europe, and (iii) tetraploids from Iceland + central Norway. Available evidence supports a stepwise differentiation of these three lineages that started at least before the last glacial maximum by processes of genome duplication, interlineage hybridization and/or allopatric evolution in distinct periglacial refugia. We reject the hypothesis of more recent postglacial speciation. Ecological characteristics of the populations under study only partly reflect genetic variation and suggest broad niches of postglacial colonizers. Despite their largely allopatric modern distributions, the north-European lineages of the G. pusillum group do not show signs of rapid postglacial divergence, in contrast to most other northern endemics. Our study suggests that plants inhabiting deglaciated areas outside the Arctic may exhibit very different evolutionary histories compared with their more thoroughly investigated high-arctic counterparts.

The impact of nitrogen deposition on acid grasslands in the Atlantic region of Europe.

A survey of 153 acid grasslands from the Atlantic biogeographic region of Europe indicates that chronic nitrogen deposition is changing plant species composition and soil and plant-tissue chemistry. Across the deposition gradient (2-44 kg N ha(-1) yr(-1)) grass richness as a proportion of total species richness increased whereas forb richness decreased. Soil C:N ratio increased, but soil extractable nitrate and ammonium concentrations did not show any relationship with nitrogen deposition. The above-ground tissue nitrogen contents of three plant species were examined: Agrostis capillaris (grass), Galium saxatile (forb) and Rhytidiadelphus squarrosus (bryophyte). The tissue nitrogen content of neither vascular plant species showed any relationship with nitrogen deposition, but there was a weak positive relationship between R. squarrosus nitrogen content and nitrogen deposition. None of the species showed strong relationships between above-ground tissue N:P or C:N and nitrogen deposition, indicating that they are not good indicators of deposition rate.