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The pantropical genus Begonia is the sixth-largest genus of flowering plants, including 1870 species. The sections of Begonia are used frequently as analogues to genera in other families but, despite their taxonomic utility, few of the current sections have been examined in the light of molecular phylogenetic analyses. We present herein the largest, most representative phylogeny of Begonia published to date and a subsequent provisional sectional classification of the genus. We utilised three plastid markers for 574 species and 809 accessions of Begonia and used Hillebrandia as an outgroup to produce a dated phylogeny. The relationships between some species and sections are poorly resolved, but many sections and deeper nodes receive strong support. We recognise 70 sections of Begonia including 5 new sections: Astrothrix, Ephemera, Jackia, Kollmannia, and Stellandrae; 4 sections are reinstated from synonymy: Australes, Exalabegonia, Latistigma and Pereira; and 5 sections are newly synonymised. The new sectional classification is discussed with reference to identifying characters and previous classifications.

BackgroundWith currently 1980 described species, the mega-diverse Begonia is now perhaps the 5th largest flowering plant genus, expanding rapidly from ca. 900 species in 1997 to its current size in merely two decades. In continuation of our studies of Asian Begonia, we report six additional new species from Guangxi, the region/province harboring the second richest Begonia flora of China.ResultsBased on morphological and molecular data, the new species B. aurora belongs to Begonia sect. Platycentrum, while the other five new species (viz. B. larvata, B. longiornithophylla, B. lui, B. scabrifolia, and B. zhuoyuniae) are members of Sect. Coelocentrum. Somatic chromosome numbers of B. longiornithophylla and B. zhuoyuniae at metaphase were counted as 2n = 30, consistent with previously reports for Sect. Coelocentrum.ConclusionsWith the addition of the six new species, the total number of Begonia species in Guangxi increases from 86 to 92. Detailed description, line drawings, and color plates are provided to aid in identification.

Aim To reconstruct the diversification history of Rhododendron sect. Brachycalyx (Ericaceae), and to elucidate the differences in evolutionary history between 18 insular and two continental species. Location Islands of Japan, South Korea and Taiwan and the mainland of China in East Asia. Methods Sequences of seven non-coding chloroplast DNA regions (3971 bp) were obtained from 74 populations covering all 20 species in Rhododendron sect. Brachycalyx. The diversification history of the section was estimated by phylogenetic analysis and molecular dating. Genetic diversity estimates within species and species groups (continental and insular species) were calculated. Differences in patterns of genetic structure within each species group were estimated by analysis of the spatial genetic structure. Results The section was monophyletic and started to diversify in the late Miocene or Pliocene. We detected 61 haplotypes in the section, of which 44 were observed in the insular species and 17 in the continental species. The two species groups were almost monophyletic. Genetic diversity across species was higher for the group of insular species than for the group of continental species, corresponding to the difference in species richness. In contrast, the insular species showed a tendency towards low genetic diversity within species and populations, whereas the continental species showed the opposite trend. Main conclusions The rapid diversification in the insular species during the Quaternary may be a result of genetic drift due to population isolation and population decline on the islands. In contrast, widespread migration or colonization may have prevented allopatric speciation in the continental species.

The Philippine island of Palawan is highly biodiverse. During fieldwork there in 2011 & 2014 we found five unknown species in the large genus Begonia. The species are similar in their rhizomatous stems, four-tepaled flowers, inferior two- or three-locular ovaries with bilamellate placentas, and are assignable to Begonia sect. Baryandra. Our observations support the recognition of these as five new species endemic to Palawan: B. elnidoensis, B. gironellae, B. quinquealata, B. tabonensis and B. tenuibracteata which are described here. The five new species were added to phylogenies based Bayesian analysis of nrDNA (ITS) and chloroplast DNA (ndhA, ndhF-rpl32, rpl32-trnL, trnC-trnD), along with 45 other allied ingroup species. A majority of the species show incongruent positions in the two phylogenies, with evidence of prevalent chloroplast capture. Models show chloroplast capture is more likely in plant populations with high levels of inbreeding following a reduction in selfing rate after hybridisation; we suggest that this is a possible explanation for the massive amount of chloroplast exchange seen in our phylogeny, as Begonia species often exist as small isolated populations and may be prone to inbreeding depression. Our data also indicate a level of nuclear genetic exchange between species. The high prevalence of hybrid events in Begonia is potentially an important factor in driving genomic change and species evolution in this mega-diverse genus.

Aim: The origin of Neotropical hyperdiversity is one of the most intriguing questions in modern biogeography and is best answered through the investigation of large, pantropically distributed genera, allowing the comparison of closely related clades in different regions. We produced a dated phylogeny and reconstructed ancestral ranges of the megadiverse, Andean-centred genus Begonia to discern its dispersal history throughout the Neotropics and correlates of range evolution. Neotropical and Palaeotropical diversification rates were estimated. Location: Neotropics: Central America, South America, West Indies and Mexico. Methods: Plastid DNA sequence data from species representing the full geographical range and majority of sections of Neotropical Begonia were analysed with a secondarily calibrated relaxed molecular clock in order to estimate the age of crown groups and divergence times within Neotropical Begonia. Ancestral areas were reconstructed with a Bayesian approach to dispersal-vicariance analysis, a likelihood framework under a dispersal-extinction-cladogenesis model, and a Bayesian binary method. Diversification rates were estimated under a Bayesian framework. Results: Biogeographical reconstruction indicated two independent trans-Atlantic colonizations of the Neotropics from Africa. Early-diverging lineages of both clades are reconstructed as having diversified in the mid-Miocene, with multiple dispersal events between the Brazilian Atlantic rain forest and the Andes, and single radiations within the West Indies and Central America plus Mexico. Main conclusions: Begonia displays numerous radiations within regions, punctuated by long-distance dispersal. Successful colonization and diversification is predicted by the presence of upland habitat. Recognizing the role of chance dispersal events between available habitats is vital for understanding the formation of current biogeographical patterns.

• Background and Aims Foliar variegation is recognized as arising from two major mechanisms: leaf structure and pigment-related variegation. Begonia has species with a variety of natural foliar variegation patterns, providing diverse examples of this phenomenon. The aims of this work are to elucidate the mechanisms underlying different foliar variegation patterns in Begonia and to determine their physiological consequences. • Methods Six species and one cultivar of Begonia were investigated. Light and electron microscopy revealed the leaf structure and ultrastructure of chloroplasts in green and light areas of variegated leaves. Maximum quantum yields of photosystem II were measured by chlorophyll fluorescence. Comparison with a cultivar of Ficus revealed key features distinguishing variegation mechanisms. • Key Results Intercellular space above the chlorenchyma is the mechanism of variegation in these Begonia. This intercellular space can be located (a) below the adaxial epidermis or (b) below the adaxial water storage tissue (the first report for any taxa), creating light areas on a leaf. In addition, chlorenchyma cell shape and chloroplast distribution within chlorenchyma cells differ between light and green areas. Chloroplasts from both areas showed dense stacking of grana and stroma thylakoid membranes. The maximum quantum yield did not differ significantly between these areas, suggesting minimal loss of function with variegation. However, the absence of chloroplasts in light areas of leaves in the Ficus cultivar led to an extremely low quantum yield. • Conclusions Variegation in these Begonia is structural, where light areas are created by internal reflection between air spaces and cells in a leaf. Two forms of air space structural variegation occur, distinguished by the location of the air spaces. Both forms may have a common origin in development where dermal tissue becomes loosely connected to mesophyll. Photosynthetic functioning is retained in light areas, and these areas do not include primary veins, potentially limiting the costs of variegation.

BackgroundWhile polyploids are common in plants, the evolutionary history and natural dynamics of most polyploid groups are still unclear. Owing to plentiful earlier systematic studies, Ludwigia sect. Isnardia (comprising 22 wetland taxa) is an ideal allopolyploid complex to investigate polyploid evolution and natural dynamics within and among taxa. With a considerable sampling, we concentrated on revisiting earlier phylogenies of Isnardia, reevaluating the earlier estimated age of the most recent common ancestor (TMRCA), exploring the correlation between infraspecific genetic diversity and ploidy levels, and inspecting interspecific gene flows among taxa.ResultsPhylogenetic trees and network concurred with earlier phylogenies and hypothesized genomes by incorporating 192 atpB-rbcL and ITS sequences representing 91% of Isnardia taxa. Moreover, we detected three multi-origin taxa. Our findings on L. repens and L. sphaerocarpa were consistent with earlier studies; L. arcuata was reported as a multi-origin taxon here, and an additional evolutionary scenario of L. sphaerocarpa was uncovered, both for the first time. Furthermore, estimated Isnardia TMRCA ages based on our data (5.9 or 8.9 million years ago) are in accordance with earlier estimates, although younger than fossil dates (Middle Miocene). Surprisingly, infraspecific genetic variations of Isnardia taxa did not increase with ploidy levels as anticipated from many other polyploid groups. In addition, the exuberant, low, and asymmetrical gene flows among Isnardia taxa indicated that the reproductive barriers may be weakened owing to allopolyploidization, which has rarely been reported.ConclusionsThe present research gives new perceptions of the reticulate evolution and dynamic nature of Isnardia and points to gaps in current knowledge about allopolyploid evolution.

• Premise of the study: One third of the species-rich Philippine flora is endemic, and most of the islands in the archipelago have never been connected to a continental region. We currently lack any well-sampled angiosperm phylogenies that span the archipelago, prohibiting the formation of informed hypotheses as to the evolution of this rich and highly endemic flora. • Methods: We produced time-calibrated phylogenetic trees from both nuclear (ITS) and chloroplast (ndhA intron, ndhF-rp132 spacer, rp132-trnL spacer, trnC-trnD spacer) regions of 41 species of Begonia sect. Baryandra, all except one endemic to the Philippines. Historical biogeography was reconstructed across the chloroplast phylogeny using a Bayesian binary method of character optimization. Comparison of phylogenies from the two genomes permitted insight into the prevalence of hybridization in the group. • Key results: The Philippine archipelago was colonized by Begonia sect. Baryandra in the late Miocene, via long-distance dispersal from western Malesia and a point of entry likely to be in the northwestern region of the archipelago. Palawan, Luzon, and Panay all bear early-branching lineages from this initial colonization. There have been Plio-Pleistocene dispersals from these islands into Borneo and Mindanao. Hybridization was common between species as evidenced by haplotype sharing and phylogenetic incongruence. • Conclusions: The phylogenies show a high degree of geographic structure, which millions of years of exposure to typhoons have not blurred, showing long-term species and population stability. The recent dispersals to Mindanao are congruent with the geologically recent arrival of the island at its current latitude in the southern Philippines.

While it is known that whole genome duplication (WGD) and reticulate evolution play important roles in plant evolution, the origins and evolutionary histories of most polyploid and reticulate groups are still poorly known. The North Temperate haplostemonous (NTH) Ludwigia L. (sections Isnardia (L.) W. L. Wagner & Hoch, Ludwigia, Microcarpium Munz, and Miquelia P. H. Raven) group, characterized by having 4-merous and haplostemonous flowers, pluriseriate and free seeds, glabrous and convex nectaries, and a north-temperate distribution, is a polyploid complex (2×, 4×, 6×, and 8×) of 24 species with frequent reports of inter- and intrasectional hybridization. Although earlier biosystematics studies postulated some evolutionary scenarios and recent molecular phylogenetic studies have partially tested these propositions, the full history of their reticulate evolution remains puzzling. In this study, we sequenced four chloroplast regions (rpL16, rpoB-trnC, trnL-trnF, and ycf6-psbM) and conducted extensive molecular cloning of the biparentally inherited single-copy nuclear PgiC gene (376 clones in total), sampling 23 of the 24 NTH Ludwigia species whose chromosome numbers and ploidy levels were confirmed. Both the chloroplast and PgiC trees include strongly supported sister clades of section Ludwigia (four diploid species) and the \"Microcarpium complex\" (composed of sections Isnardia, Microcarpium, and Miquelia), which together are sister to the rest of Ludwigia. In the PgiC tree, eight clades are identified within the Microcarpium complex, with four clades including no extant diploid species. Neither sections Isnardia nor Microcarpium are monophyletic, while the monospecific section Miquelia has a hybrid origin. By integrating our phylogenetic trees with previous cytological hypotheses, the reticulate evolution of NTH Ludwigia is disentangled and four to eight extinct diploid species are inferred. Ancestral area reconstruction supports a North American origin of L. ovalis whose current East Asian distribution reflects a relict of the Arcto-Tertiary Geoflora. Based on our results, we propose to synonymize sections Microcarpium and Miquelia under the expanded section Isnardia.

BackgroundSino-Vietnamese limestone karsts (SVLK) are a biodiversity hotspot rich in endemic plant species associated with caves and cave-like microhabitats. Based on phylogenetic studies of Begonia sect. Coelocentrum, a species-rich and characteristic SVLK clade, geographic isolation caused by extensive and continuous karstification was proposed as the major driving force triggering population diversification and geographic speciation. To test this proposition, population genetics and phylogeography of Begonia luzhaiensis were investigated using EST-SSR markers and the chloroplast trnC-ycf6 intergenic spacer.ResultsF statistics, Bayesian clustering analysis, AMOVA, and PCoA of both data sets all indicated substantial population differentiation and significant isolation by distance. Nested clade phylogeographic analyses inferred that historical fragmentations have been prominent, congruent with Guangxi’s geohistory of karstification as well as suggesting a mountain chain in northeastern Guangxi could have also acted as a major geographic barrier. A Bayesian skyline plot (BSP) indicated a slight decline in effective population size at 75,000 years ago (75 Kya), coinciding with the last glacial period during which the increased aridity in East Asia had retarded karstification, negatively affecting the populations of B. luzhaiensis. However, BSP detected a continuous and further population decline until the present time even though summer monsoons have resumed since the end of the last glacial maximum.ConclusionsThe microevolution patterns of B. luzhaiensis support that limited gene flow would have greatly enhanced the effects of random genetic drift and has been a major factor promoting diversification in Begonia, highly congruent with previous proposition. Based our study, we further propose that the arrival of Paleolithic Homo sapiens whose activities centered around limestone caves could have had further impacts on the populations of B. luzhaiensis, resulting in additional population decline. Further habitat destruction could have resulted from the transition from hunter gathering to food-producing societies ca. 20–10 Kya and the development of agriculture ca. 10 Kya in South China. Implications of the current study for SVLK plant conservation are also discussed.