Jian-Wen Zhang

Does the Arcto-Tertiary Biogeographic Hypothesis Explain the Disjunct Distribution of Northern Hemisphere Herbaceous Plants? The Case of Meehania (Lamiaceae)

Despite considerable progress, many details regarding the evolution of the Arcto-Tertiary flora, including the timing, direction, and relative importance of migration routes in the evolution of woody and herbaceous taxa of the Northern Hemisphere, remain poorly understood. Meehania (Lamiaceae) comprises seven species and five subspecies of annual or perennial herbs, and is one of the few Lamiaceae genera known to have an exclusively disjunct distribution between eastern Asia and eastern North America. We analyzed the phylogeny and biogeographical history of Meehania to explore how the Arcto-Tertiary biogeographic hypothesis and two possible migration routes explain the disjunct distribution of Northern Hemisphere herbaceous plants. Parsimony and Bayesian inference were used for phylogenetic analyses based on five plastid sequences (rbcL, rps16, rpl32-trnH, psbA-trnH, and trnL-F) and two nuclear (ITS and ETS) gene regions. Divergence times and biogeographic inferences were performed using Bayesian methods as implemented in BEAST and S-DIVA, respectively. Analyses including 11 of the 12 known Meehania taxa revealed incongruence between the chloroplast and nuclear trees, particularly in the positions of Glechoma and Meehania cordata, possibly indicating allopolyploidy with chloroplast capture in the late Miocene. Based on nrDNA, Meehania is monophyletic, and the North American species M. cordata is sister to a clade containing the eastern Asian species. The divergence time between the North American M. cordata and the eastern Asian species occurred about 9.81 Mya according to the Bayesian relaxed clock methods applied to the combined nuclear data. Biogeographic analyses suggest a primary role of the Arcto-Tertiary flora in the study taxa distribution, with a northeast Asian origin of Meehania. Our results suggest an Arcto-Tertiary origin of Meehania, with its present distribution most probably being a result of vicariance and southward migrations of populations during climatic oscillations in the middle Miocene with subsequent migration into eastern North America via the Bering land bridge in the late Miocene.

Cytological study on the genus Syncalathium (Asteraceae-Lactuceae), an endemic taxon to alpine scree of the Sino-Himalayas

Abstract  Cytological characters of four species in Syncalathium (Asteraceae: Lactuceae), a small genus with six identified species endemic to alpine scree of the Sino‐Himalayan region, are surveyed in this report. Three species (Syncalathium pilosum, Syncalathium chrysocephalum, and Syncalathium disciforme) are examined for the first time. Combined with our previous counts, five species have been cytologically investigated from the genus and the results indicated that all species are diploid with the basic somatic chromosome number of x=8. The karyotype asymmetry of Syncalathium souliei is 2A, distinct from the other four species of 1A, and the remaining species are divided into two subgroups with different karyotypes, consistent with their morphological features. The significance of the cytological evolution of Syncalathium is briefly discussed.

Origins and Evolution of Plant Diversity in the Hengduan Mountains, China

The Hengduan Mountains region (HDM) in southwest China, one of the earths 34 biodiversity hotspots, is characterized by its unique geology, dramatic topography, a climate where snow and below freezing temperatures can occur on any day of the year, by its location at elevations averaging between (1400–) 2000 and 4500 (–5300) meters above sea level (m a.s.l.), and by one of the richest floras in the temperate Northern Hemisphere. The formation and evolution of the plant diversity in the area and uplift of the Qinghai–Tibet Plateau (QTP) were synchronous (Sun, 2002, Sun and Li, 2003). During its geological history, as part of the QTP, the area was still below the Tethys Sea or on the coast of the Tethys in the late Cretaceous (Zhang, 2012). In the early Tertiary, the collision between the Indian plate and Eurasia led to the retreat of the Tethys Sea and the QTP entered an era of land evolution (Zheng, 2013). From the Eocene to the Oligocene, the Tethys gradually narrowed as the Indian plate continued its northward movement. By the end of the Oligocene, the sea had since dropped out and the main body of the QTP was transformed into a land environment (Zhang, 2012). The Hengduan Mountains (the eastern edge of the QTP) had formed as north–south asymmetric wavy creases and large intervening fault zones (gorges). The geological evolution of the HDM coincided with the uplift process and was synchronous with the evolution of the QTP (Zhang, 2012). Therefore, the flora of the HDM began its development and evolution with the retreat of the Tethys Sea and appearance of land in the early Paleogene. Along with the uplift of the QTP and the evolution of the geological environment, the flora underwent a change from a thermophilic flora in the early Paleogene to a xerophytic and temperate to alpine flora by the mid-to late Neogene (Sun, 2002). Additionally, many plant groups migrated into the region from various sources resulting in a very rich and complex flora, which the HDM has preserved in many ways to the present. After the Neogene, global temperatures decreased, resulting in the Quaternary glacial periods. Plant diversity and the flora of the Arctic-Tertiary in many parts of the Northern Hemisphere, such as in Europe and N America, suffered devastating destruction and a large number of species became extinct, resulting in the extant flora in these regions becoming poor and reduced to fragments of their former richness (Kubitzki and Krutzsch, 1996, Tiffney and Manchester, 2001). It is therefore difficult for us to study the origin, differentiation and formation mechanisms of plant diversity of the earth in those areas. The complex and diverse habitats in the HDM, however, were relatively little affected by climatic and geological processes. They therefore provided optimal conditions for evolution and diversification to take place while at the same time maintaining refugia where plants could ride out the glacial cycles. The synchronous evolution of plant diversity and geological events provide a relatively integrated framework for interpreting the evolutionary history of the flora. Not only are there some ancient remnants or relics, but also, more prominently, a large number of clades that experienced rapid radiations, forming relatively complete lineages and many young species and infraspecific taxa. The HDM is therefore not only a natural historical ‘museum’ that has preserved plant diversity since the Cenozoic era, but also a ‘cradle’ where many new species were born and flourished. The preservation of the old while giving rise to the new has resulted in the incredible plant diversity that has made the HDM the hotspot that it is today and the key area and natural laboratory for the study of the origins, evolution and dispersal of that diversity.

Climatic Factors Drive Population Divergence and Demography: Insights Based on the Phylogeography of a Riparian Plant Species Endemic to the Hengduan Mountains and Adjacent Regions.

Quaternary climatic factors have played a significant role in population divergence and demography. Here we investigated the phylogeography of Osteomeles schwerinae, a dominant riparian plant species of the hot/warm-dry river valleys of the Hengduan Mountains (HDM), Qinling Mountains (QLM) and Yunnan-Guizhou Plateau (YGP). Three chloroplast DNA (cpDNA) regions (trnD-trnT, psbD-trnT, petL-psbE), one single copy nuclear gene (glyceraldehyde 3-phosphate dehydrogenase; G3pdh), and climatic data during the Last Interglacial (LIG; c. 120–140 ka), Last Glacial Maximum (LGM; c. 21 ka), and Current (c. 1950–2000) periods were used in this study. Six cpDNA haplotypes and 15 nuclear DNA (nDNA) haplotypes were identified in the 40 populations of O. schwerinae. Spatial Analysis of Molecular Variance, median-joining networks, and Bayesian phylogenetic trees based on the cpDNA and nDNA datasets, all suggested population divergence between the QLM and HDM-YGP regions. Our climatic analysis identified significant heterogeneity of the climatic factors in the QLM and HDM-YGP regions during the aforementioned three periods. The divergence times based on cpDNA and nDNA haplotypes were estimated to be 466.4–159.4 ka and 315.8–160.3 ka, respectively, which coincide with the time of the weakening of the Asian monsoons in these regions. In addition, unimodal pairwise mismatch distribution curves, expansion times, and Ecological Niche Modeling suggested a history of population expansion (rather than contraction) during the last glaciation. Interestingly, the expansion times were found being well consistent with the intensification of the Asian monsoons during this period. We inferred that the divergence between the two main lineages is probably caused by disruption of more continuous distribution because of weakening of monsoons/less precipitation, whilst subsequent intensification of the Asian monsoons during the last glaciation facilitated the expansion of O. schwerinae populations.

Role of the Qinghai-Tibetan Plateau uplift in the Northern Hemisphere disjunction: evidence from two herbaceous genera of Rubiaceae

To assess the role of the Qinghai-Tibetan Plateau uplift in shaping the intercontinental disjunction in Northern Hemisphere, we analyzed the origin and diversification within a geological timeframe for two relict herbaceous genera, Theligonum and Kelloggia (Rubiaceae). Phylogenetic relationships within and between Theligonum and Kelloggia as well as their relatives were inferred using five chloroplast markers with parsimony, Bayesian and maximum-likelihood approaches. Migration routes and evolution of these taxa were reconstructed using Bayesian relaxed molecular clock and ancestral area reconstruction. Our results suggest the monophyly of each Theligonum and Kelloggia. Eastern Asian and North American species of Kelloggia diverged at ca.18.52 Mya and the Mediterranean species of Theligonum diverged from eastern Asian taxa at ca.13.73 Mya. Both Kelloggia and Theligonum are Tethyan flora relicts, and their ancestors might have been occurred in warm tropical to subtropical environments along the Tethys coast. The Qinghai-Tibetan Plateau separated the eastern and western Tethyan area may contribute significantly to the disjunct distributions of Theligonum, and the North Atlantic migration appears to be the most likely pathway of expansion of Kelloggia to North America. Our results highlight the importance role of the QTP uplift together with corresponding geological and climatic events in shaping biodiversity and biogeographic distribution in the Northern Hemisphere.

Systematic significance of cytology in Cyananthus (Campanulaceae) endemic to the Sino‐Himalayan region

Chromosome numbers and the morphology of members of 24 populations representing 15 species of the Sino‐Himalayan endemic genus Cyananthus (Campanulaceae) were studied using karyological and numerical taxonomic techniques. The chromosome numbers of these taxa are 2n = 10, 12, 14, 24, 28, and the basic chromosome numbers for the genus are x = 5, 6, 7. All species except C. inflatus Hook. f. & Thoms. and C. microphyllus Edgew. were examined for the first time and a new ploidy level (tetraploidy) is reported in the genus. Chromosome measurement data were analyzed using cluster analysis. The relationships between three sections within Cyananthus and evolutionary trends within the genus are discussed in the light of karyological data. The cytological data suggest that Cyananthus is a relatively primitive genus in Campanulaceae and there is significant division within the genus, and polyploidization may have played an important role in the chromosome evolution and speciation of Cyananthus in the Himalayan–Hengduan Mountains.

Karyotypes of nineteen species of Asteraceae in the Hengduan Mountains and adjacent regions

The Hengduan Mountains region is a biodiversity hotspot. In this study, we report the karyotypes of 19 species (21 populations) of Asteraceae from this region, 14 of which are reported for the first time. We also examined polyploidy in Asteraceae plants and summarized karyotype data in the literature for 69 congeneric taxa. In these genera, there were five different ploidy levels in the region, though the most dominant was diploid (73.08%). There is no direct evidence that ploidy level and karyotype asymmetry are associated with the distribution of recorded Asteraceae species from the Hengduan Mountains. This suggests that polyploidy (26.92%) may not play an important role in the evolutionary history of these plants, even though, among these genera, the ratio of paleopolyploidy was high (46.15%).

Phylogeography of Parasyncalathium souliei (Asteraceae) and Its Potential Application in Delimiting Phylogeoregions in the Qinghai-Tibet Plateau (QTP)-Hengduan Mountains (HDM) Hotspot

Biogeographic regionalization can help to better understand diversity in biogeography, conservation, and macroecology. Historical regionalization schemes typically focus on species distributions, often rarely considering the rich context that phylogeographic information can provide. We investigated whether phylogeographic data could help to delineate floristic regions in the Qinghai-Tibet Plateau (QTP)-Hengduan Mountains (HDM) region by analyzing phylogeographic structure in the herb Parasyncalathium souliei (Asteraceae). We sequenced the plastid psbA-trnH and trnL-rpl32 spacer regions for 417 individuals in 36 populations across the geographic range of the species. To estimate the phylogeographic history of this species, a series of population genetic, phylogenetic, molecular dating, and haplotype network analyses were conducted, as were tested for historical demographic expansions. Using occurrence data, species distribution modeling was used to estimate geographic distributions at three time points: the present, the Mid-Holocene and the Last Glacial Maximum. Significant phylogeographic structure was evident (NST> GST; P < 0.05) among the 37 haplotypes detected. Four major haplogroups were identified based on phylogenetic analyses. Private haplotypes were restricted to geographically distinct regions that generally corresponded to previously identified biogeographic subregions within the QTP-HDM region. Our results imply Pliocene-Pleistocene diversification of P. souliei and suggest that the species may have been geographically widespread early in its history. This study may provide valuable evidence for phylogeographic regionalization using chloroplast genetic data in a common, widespread endemic species from the QTP-HDM.

Plastome phylogenomics of the early-diverging eudicot family Berberidaceae

The relationships among the genera of the early-diverging eudicot family Berberidaceae have long been controversial. To resolve these relationships and to better understand plastome evolution within the family, we sequenced the complete plastome sequences of ten Berberidaceae genera, combined these with six existing plastomes for the family, and conducted a series of phylogenomic analyses on the resulting data set. Five of the newly sequenced plastomes were found to possess the typical angiosperm plastome complement of 79 protein-coding genes, 4 rRNA genes, and 30 tRNA genes. The infA gene was found to be pseudogenized in Bongardia, Diphylleia, Dysosma and Vancouveria; rps7 was found to be severely truncated in Diphylleia, Dysosma and Podophyllum; clpP was found to be highly divergent in Vancouveria; and a ∼19 kb inversion was detected in Bongardia. Maximum likelihood phylogenetic analyses of a 79-gene, 24-taxon data set including nearly all genera of Berberidaceae recovered four chromosome groups (x = 6, 7, 8, 10), resolved the x = 8 group as the sister to the x = 10 group, and supported the monophyly of the clade comprising x = 7, 8, 10. The generic relationships within each group were all resolved with high support. Based on gene presence within the Inverted Repeat (IR), a total of seven plastome IR types were identified within Berberidaceae. Biogeographical analysis indicated the origin and diversification of Berberidaceae has likely been strongly influenced by the distribution of its favored habitat: temperate forests.

Mazus sunhangii (Mazaceae), a New Species Discovered in Central China Appears to Be Highly Endangered.

Mazus sunhangii, a new species of Mazaceae from central China is described and illustrated based on evidence from morphology and molecular phylogeny. This new species is morphologically similar to M. puchellus and M. omeiensis but differs in erect habit, inflorescence position, leaf pattern and corolla color. Phylogenetic analysis based on four chloroplast DNA regions (rbcL, rps16, trnL-F, and psbA-trnH) identified the new species as the independent lineage sister to the other East Asian Mazus species. The new species is known only from a single location in Mt. Shennongjia area in northwest Hubei province, at the elevation of 760 m. The species grows on the limestone cliff, and, because a tourist arterial highway is located along this cliff, its habitat can be easily disturbed or destroyed. We propose that the only known species location is recognized as critical habitat (i.e., as the habitat required to ensure the persistence of a species) and the species listed as Critically Endangered based on the International Union for Conservation of Nature Red List Categories and Criteria B2a.