Search

The prolonged interplay between orographic and climatic changes creates biogeographic barriers, resulting in the allopatric differentiation of plants in the Himalaya–Hengduan Mountains. Such consequences have led us to investigate the long-term Neogene–Quaternary geo-climatic history of the Eastern Himalaya–Hengduan Mountains. Narrowly distributed populations of Koenigia forrestii were sampled (ten populations, 97 individuals) and analysed for their genetic architecture, including phylogenetic reconstruction (based on plastome and plastid DNA/nuclear regions), molecular dating and demography, in combination with niche dynamics. We estimated that K. forrestii (stem age: 11.39 Mya) diverged into three non-overlapping distributed lineages during the Neogene–Quaternary periods (5.84–2.57 Mya), with Eastern Himalaya (EHa) being the first and most diverse lineage. 'Isolation by environment' revealed the existence of genetic structures that were significantly affected by the disparate environment. The presence of demographic events is well supported by the Bayesian skyline plot, indicating recent demographic expansion. Hence, lineage divergence and differentiation were mainly triggered by the heterogeneous environment associated with the biogeographic barriers due to the Tsangpo-Brahmaputra Grand Canyon, Mekong-Salween Divide and local mountain systems. Nevertheless, niche shift and local adaptation are the keys to determining the genetic architecture, demographic dynamics and diversification history of K. forrestii. [ABSTRACT FROM AUTHOR]

It has been hypothesized that geological and climatic changes in the Sino–Himalayan region played a significant role in evolutionary history. In this study, we tested this hypothesis by investigating the phylogeography of Excoecaria acerifolia (Euphorbiaceae), a riparian plant species that is widely distributed in the hot/warm-dry river valleys of the Sino–Himalayan region. Spatial analysis of molecular variance, a median-joining network and a Bayesian phylogenetic tree based on plastid DNA, all suggested three major lineages corresponding to the Jialing-Min-Dadu (JMD lineage), Jinsha-Yalong-Salween (JY lineage) and Yarlung Tsangpo-Mekong-Red-Nanpan (YMRN lineage) drainage basins. This was also generally supported by the results based on nuclear DNA. The divergence times of these three major lineages based on both datasets fell in the early Pleistocene, coinciding with the period of drainage reorganization events in the Sino–Himalayan region. The diversification times in the lineages were, however, dated back to the mid Pleistocene, corresponding to the Naynayxungla glaciation (0.72–0.50 Mya) and the penultimate glaciation (0.30–0.13 Mya), which were the most and second most severe glaciations in this region, respectively. Furthermore, mismatch analyses, neutrality test and ecological niche modelling suggest long-term demographic stability of the JY and JMD populations, with expansion only in the YMRN populations during the period(s) from the late penultimate glaciation (138.12 Kya) to the Last Interglacial (95.79 Kya), probably because of less extensive glaciations since the late Pleistocene and the gradually warming interglacial stage. Our study provides one of the few pieces of evidence indicating that combined historical drainage reorganization and climatic change since the Pleistocene might also have acted as important factors in the evolutionary history of riparian plants in the region. [ABSTRACT FROM AUTHOR]

Environmental conditions are known to affect the reproductive fitness of insects, as do host plants. Although the highly specialized bracts of Himalayan 'glasshouse' plants are thought to be an adaptive morphology that allows the plant to reproduce in harsh alpine environments, little information appears to exist concerning the benefit of these bracts for the pollinating insects. In this study, we examine whether the semi-translucent bracts of R heum alexandrae, a giant herb endemic to the alpine zone of the Hengduan Mountains in south-western China, enhance the reproductive fitness of its pollinator. R heum alexandrae depends mainly on mutualistic seed-consuming B radysia flies for pollination. Bracts increased interior temperature on sunny days, acted as a buffer against fluctuating air humidity, greatly decreased the intensities of ultraviolet B/ C radiation and provided shelter from strong winds. Bract removal significantly decreased adult oviposition and offspring performance of pollinators during flowering and fruiting, respectively. Our results indicate that the bracts of R. alexandrae enhance the reproductive fitness of its pollinating seed-consuming mutualist in alpine environments, which may be attributed to the positive effects of the bracts on the interior microenvironment. © 2015 The Linnean Society of London, B otanical J ournal of the L innean S ociety, 2015, 179, 349-359. [ABSTRACT FROM AUTHOR]

The systematic significance of the morphological structure of achenes in the Himalayan- Tibetan Plateau endemic genera Soroseris, Syncalathium and Parasyncalathium is described and discussed. The achene surface sculpturing of 15 samples representing 13 species of the three genera was investigated using scanning electronic microscopy ( SEM) to evaluate inter- and intrageneric relationships of the three genera. Characters such as cell arrangement, shape of the epidermis, type of ornamentation of the outer cell wall and degree of wax development are described. The results show that characters such as the shape of the epidermis and the type of ornamentation of the outer cell wall are distinct between the three genera and useful for species-level classification. Parasyncalathium souliei differs from Syncalathium, in which it has traditionally been placed, in the short, stout beak of the achene and especially in the obscure outline of the epidermal cells and their long acuminate, steeple-like, end walls. Combined with karyological and molecular data, the differences in achene morphology and sculpturing further support our recognition of Parasyncalathium as distinct from Syncalathium. The achene characters are not only useful for assessing relationships, but are also useful for delimiting species. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 476-486. [ABSTRACT FROM AUTHOR]

Mitchella is a small genus of the Rubiaceae with only two species. It is the only herbaceous semishrub of the family showing a disjunct distribution in eastern Asia and eastern North America, extending to Central America. Its phylogeny and biogeographical diversification remain poorly understood. In this study, we conducted phylogenetic and biogeographical analyses for Mitchella and its close relative Damnacanthus based on sequences of the nuclear internal transcribed spacer ( ITS) and four plastid markers ( rbcL, atpB-rbcL, rps16 and trnL-F). Mitchella is monophyletic, consisting of an eastern Asian M. undulata clade and a New World M. repens clade. Our results also support Michella as the closest relative to the eastern Asian Damnacanthus. The divergence time between the two intercontinental disjunct Mitchella species was dated to 7.73 Mya, with a 95% highest posterior density ( HPD) of 3.14−12.53 Mya, using the Bayesian relaxed clock estimation. Ancestral area reconstructions suggest that the genus originated in eastern Asia. The semishrub Mitchella appears to have arisen from its woody ancestor in eastern Asia and then migrated to North America via the Bering land bridge in the late Miocene. © 2013 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Phylogenetic analyses were conducted for Astilbe ( Saxifragaceae), an Asian/eastern North American disjunct genus, using sequences of nuclear ribosomal internal transcribed spacer ( ITS) and plastid mat K, trnL-trn F and psb A-trnH regions. The monophyly of Astilbe is well supported by both ITS and plastid sequences. Topological incongruence was detected between the plastid and the ITS trees, particularly concerning the placement of the single North American species, A. biternata, which may be most probably explained by its origin involving hybridization and/or allopolyploidy with plastid capture. In Astilbe, all species with hermaphroditic flowers constitute a well-supported clade; dioecious species form a basal grade to the hermaphroditic clade. Astilbe was estimated to have split with Saxifragopsis from western North America at 20.69 Ma (95% HPD: 12.14-30.22 Ma) in the early Miocene. This intercontinental disjunction between Astilbe and Saxifragopsis most likely occurred via the Bering land bridge. The major clade of Astilbe (all species of the genus excluding A. platyphylla) was inferred to have a continental Asian origin. At least three subsequent migrations or dispersals were hypothesized to explain the expansion of Astilbe into North America, Japan and tropical Asian islands. The intercontinental disjunct lineage in Astilbe invokes a hybridization event either in eastern Asia or in North America. This disjunction in Astilbe may be explained by a Beringian migration around 3.54 Ma (95% high posterior density: 1.29-6.18 Ma) in the late Tertiary, although long-distance dispersal from eastern Asia to North America is also likely. The biogeographical connection between continental Asia, Taiwan, the Philippines and other tropical Asian islands in Astilbe provides evidence for the close floristic affinity between temperate or alpine south-western China and tropical Asia. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, ●●, ●●-●●. [ABSTRACT FROM AUTHOR]

The karyotypes of six species of Solms-laubachia and one each of Parrya and Desideria (Brassicaceae) from the Himalayan-Hengduan Mountains (Tibet, Sichuan and Yunnan provinces) were investigated. Chromosome counts of S. xerophyta, S. lanata, S. platycarpa and D. baiogoinensis are reported for the first time and found to be diploid with 2n = 14. Diploid counts were also made of S. retropilosa, a species previously known to be a tetraploid. The karyotype formulae of D. baiogoinensis, S. eurycarpa, S. pulcherrima, S. retropilosa, S. xerophyta and S. platycarpa are 2n = 14 = 6 m + 6sm + 2st, whereas those of S. lanata and P. nudicaulis are 2n = 14 = 6 m + 2sm + 6st and 2n = 14 = 8 m + 4sm + 2st, respectively. Karyotypes and counts of S. eurycarpa and S. pulcherrima are in agreement with prior studies. The relationships within Solms-laubachia and among the three genera are discussed. Speciation within Solms-laubachia may have been the result of primarily intrachromosomal variation at the diploid level, and the genus probably evolved within the Himalayan-Hengduan Mountains instead of migrating from other regions. [ABSTRACT FROM AUTHOR]