Phylogeny and Phytogeography of Eupatorium (Eupatorieae, Asteraceae): Insights from Sequence Data of the nrDNA ITS Regions and cpDNA RFLP

Eupatorium were examined by sequencing the internal transcribed spacers (ITS) of nuclear ribosomal DNA and restriction site analysis of chloroplast DNA. Molecular data provided strong evidence that (1) this genus originated in North America, (2) the genus diverged into three morphological species groups, Eutrochium, Traganthes and Uncasia in North America, and (3) one of the North American Uncasia lineages migrated into temperate Europe and eastern Asia over the Bering land bridge. The estimated divergence times support a late Miocene to early Pliocene migration from North America to Eurasia via the Bering land bridge. A European species was sister to all of the eastern Asian species examined. The disjunct distribution pattern of the genus Eupatorium is incongruent with the classical Arcto-Tertiary geoflora concept. Received 13 September 1999/ Accepted in revised form 4 January 2000     

Biology and morphology of the immature stages of Hermeuptychia atalanta (Lepidoptera: Nymphalidae: Satyrinae)

This paper describes the morphology of the immature stages (egg, larva and pupa) and larval behavior of the butterfly Hermeuptychia atalanta, a common and widespread species of satyrinae in South America. Eggs are white and spherical, laid singly on leaves of grasses. The first instar has a light-green body and dark-brown head; all remaining instars present body and head capsule light green. Larvae have no spines, and general morphology is similar to other species of the subtribe Euptychiina.     

Molecular phylogeny and biogeography of Astilbe (Saxifragaceae) in Asia and eastern North America

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 matK, trnL‐trnF and psbA‐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, ●● , ●●–●●.     

Phylogenetic assessment and biogeographic analyses of tribe <Emphasis Type="Italic">Peracarpeae</Emphasis> (Campanulaceae)

Peracarpeae is a small tribe consisting of three genera: Homocodon, Heterocodon and Peracarpa, with a disjunct distribution between eastern Asia and western North America. Homocodon is endemic to southwestern China and was previously placed in the western North American genus Heterocodon. Our phylogenetic analysis using four plastid markers (matK, atpB, rbcL and trnL-F) suggests the polyphyly of Peracarpeae. Homocodon is sister to a clade consisting of the eastern Asian Adenophora, Hanabusaya and species of Campanula from the Mediterranean region and North America, rather than forming a clade with Heterocodon. Homocodon and its Eurasia relatives are estimated to have diverged in the early Miocene (16.84 mya, 95% HPD 13.35–21.45 mya). The eastern Asian Peracarpa constitutes a clade with the North American Heterocodon, Githopsis and three species of Campanula, supporting a disjunction between eastern Asia and North America in Campanulaceae. The Asian-North American disjunct lineages diverged in the early Miocene (16.17 mya, 95% HPD 13.12–20.9 mya). The biogeographic analyses suggest that Homocodon may be a relict of an early radiation in eastern Asia, and that Peracarpa and its closest North American relatives most likely originated from a Eurasian ancestor.     

Phylogenomics,biogeography, and evolution of morphology and ecological niche of the eastern Asian–eastern North American Nyssa (Nyssaceae)

Nyssa (Nyssaceae, Cornales) represents a classical example of the well‐known eastern Asian–eastern North American floristic disjunction. The genus consists of three species in eastern Asia, four species in eastern North America, and one species in Central America. Species of the genus are ecologically important trees in eastern North American and eastern Asian forests. The distribution of living species and a rich fossil record of the genus make it an excellent model for understanding the origin and evolution of the eastern Asian–eastern North American floristic disjunction. However, despite the small number of species, relationships within the genus have remained unclear and have not been elucidated using a molecular approach. Here, we integrate data from 48 nuclear genes, fossils, morphology, and ecological niche to resolve species relationships, elucidate its biogeographical history, and investigate the evolution of morphology and ecological niches, aiming at a better understanding of the well‐known EA–ENA floristic disjunction. Results showed that the Central American (CAM) Nyssa talamancana was sister to the remaining species, which were divided among three, rapidly diversified subclades. Estimated divergence times and biogeographical history suggested that Nyssa had an ancestral range in Eurasia and western North America in the late Paleocene. The rapid diversification occurred in the early Eocene, followed by multiple dispersals between and within the Erasian and North American continents. The genus experienced two major episodes of extinction in the early Oligocene and end of Neogene, respectively. The Central American N. talamancana represents a relic lineage of the boreotropical flora in the Paleocene/Eocene boundary that once diversified in western North America. The results supported the importance of both the North Atlantic land bridge and the Bering land bridge (BLB) for the Paleogene dispersals of Nyssa and the Neogene dispersals, respectively, as well as the role of Central America as refugia of the Paleogene flora. The total‐evidence‐based dated phylogeny suggested that the pattern of macroevolution of Nyssa coincided with paleoclimatic changes. We found a number of evolutionary changes in morphology (including wood anatomy and leaf traits) and ecological niches (precipitation and temperature) between the EA–ENA disjunct, supporting the ecological selection driving trait evolutions after geographic isolation. We also demonstrated challenges in phylogenomic studies of lineages with rapid diversification histories. The concatenation of gene data can lead to inference of strongly supported relationships incongruent with the species tree. However, conflicts in gene genealogies did not seem to impose a strong effect on divergence time dating in our case. Furthermore, we demonstrated that rapid diversification events may not be recovered in the divergence time dating analysis using BEAST if critical fossil constraints of the relevant nodes are not available. Our study provides an example of complex bidirectional exchanges of plants between Eurasia and North America in the Paleogene, but “out of Asia” migrations in the Neogene, to explain the present disjunct distribution of Nyssa in EA and ENA.     

Description of Hydrobius orientalis sp. n., the first species of the subtribe Hydrobiusina from the Oriental Region (Coleoptera: Hydrophilidae: Hydrophilini)

The first Oriental species of the water scavenger beetle subtribe Hydrobiusina, Hydrobius orientalis sp. n., is described and illustrated from Guandong Province, China. It is unique in the subtribe by lacking elytral serial punctures. The species appears most closely related to Hydrobius melaenus (Germar, 1824) of eastern North America.     

The Phytogeography of the extinct angiosperm Nordenskioeldia (Trochodendraceae) and its response to climate changes

Elucidating the spatio-temporal distributions of terrestrial plants is a key for interpreting the origin of distribution patterns and the tempo of intercontinental disjunction. Nordenskioeldia was distributed in eastern Asia and North America from the Late Cretaceous to the Miocene. Its fossil record provides important information on former patterns of disjunction and dispersal in the Northern Hemisphere. New specimens from the Paleocene of China allow us to further extend the history of the group and provide the impetus to review its distribution in space and time. The comparative morphological survey on fossil Nordenskioeldia found in the Paleocene sediments in both eastern Asia and North America confirms that they belonged to the same morpho-species, which indicates a close floristic continuity between both continents due to land connection available during that time. The spatio-temporal distributions of Nordenskioeldia indicate that the taxon probably expanded eastward from eastern Asia into North America by the end of Early/Middle Maastrichtian, subsequently colonized Greenland, northeastern North America and Spitsbergen in the Early Paleocene, and finally became extinct in the Miocene. The fluctuations in its northern limits took place in response to climate changes: warming from the Paleocene to the Eocene, cooling during the Eocene–Oligocene and amelioration during the Late Oligocene–Mid-Miocene.     

Phylogenetics and biogeography of eastern Asian–North American disjunct genus Pachysandra (Buxaceae) inferred from nucleotide sequences

Abstract Pachysandra is an eastern Asian–North American disjunct genus with three species, two in eastern Asia (Pachysandra axillaris and Pachysandra terminalis) and one in eastern North America (Pachysandra procumbens). Although morphological and cytological studies suggest a close affinity of P. procumbens with P. axillaris, molecular data from nuclear and chloroplast DNA regions have provided conflicting signals. In this study, we tested previous phylogenetic hypotheses using sequences of nuclear ribosomal DNA internal transcribed spacers and chloroplast ndhF gene from multiple individuals of each of the three species. We also estimated the time of divergence between eastern Asia and eastern North America. Our results support the morphological and cytological conclusion that P. procumbens is more closely related to P. axillaris than to P. terminalis. The estimated time of divergence of P. axillaris and P. procumbens was 14.6±5.5 mya, consistent with estimates from many other eastern Asian–North American disjunct genera. The migration of Pachysandra populations from eastern Asia to North America might have occurred by way of the North Atlantic land bridge.     

Molecular phylogenetics and biogeography of the eastern Asian–eastern North American disjunct Mitchella and its close relative Damnacanthus (Rubiaceae,Mitchelleae)

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     

Phylogenetic relationships,biogeography and diversification of Coenonymphina butterflies (Nymphalidae: Satyrinae): intercontinental dispersal of a southern Gondwanan group?

The origins, evolutionary history and diversification of the Australian butterfly fauna are poorly known and uncertain. Two competing hypotheses have been proposed to explain the occurrence of butterflies on this isolated continental landmass. The common view is that all Australian butterflies entered the continent relatively recently from the northern hemisphere via Southeast Asia and/or mainland New Guinea (i.e. northern dispersal origin hypothesis). The alternative view is that part or all of the Australian butterfly fauna ultimately evolved in remnant or Southern Gondwana when Australia was connected to South America through Antarctica (i.e. Southern Gondwanan origin hypothesis). However, robust phylogenies with strong support for monophyly are lacking for the majority of Australian endemic butterfly lineages, thereby precluding determination of their systematic relationships and hence their geographic origins. Here, we use molecular data to reconstruct phylogenetic relationships of the globally distributed butterfly subtribe Coenonymphina (Satyrinae: Satyrini). This group represents a major component of the butterfly fauna of the wider Australasian region, with 19 genera and 71 species endemic to the region. Dating estimates extrapolated from secondary calibration sources indicate that the subtribe arose c . 48 Ma (95% credibility interval, 52–42 Ma), and the crown group first diverged in the Eocene (c . 44 Ma, 95% credibility interval 51–37 Ma). Rapid speciation events subsequently followed around the Eocence–Oligocene boundary, resulting in a near‐hard polytomy comprising short basal branches with nodes that are difficult to resolve. Based on strongly supported phylogenetic relationships and estimates of divergence times, we conclude that the group probably had its origin in the fragment of Southern Gondwana consisting of Australia, Antarctica and South America. However, we are unable to rule out the northern dispersal scenario, particularly as Coenonymphina are closely related to a set of predominantly Asian lineages. Dispersal and extinction events following the final break‐up of Gondwana have played a pivotal role in shaping the extant distributions of the group.     

EOCENE FLORAL EVIDENCE OF LAURACEAE: CORROBORATION OF THE NORTH AMERICAN MEGAFOSSIL RECORD

Numerous megafossils of Lauraceae have been reported from the early Tertiary of North America, but the subfamilial affinities are usually not well understood due to the great morphological variability found in extant taxa. The flowers of Androglandula tennessensis gen. et sp. nov. Taylor, from the Middle Eocene Claiborne Formation, are six-parted, pedicellate, bracteate, and have stamens with paired basal staminal glands. The flowers have ethereal oil cells and paracytic stomates throughout. The fossil species has affinities with the subtribe Cinnamomineae, and this supports suggestions that the Middle Eocene climate of the southeastern U.S. was subtropical. The existence of this fossil, and reports of the subtribe from the Eocene of Europe, indicate a South American-North American-European-southeast Asian paleodistribution suggesting that extinction in North America and Europe was the cause of the tribe's current disjunct distribution.     

Phylogenetic Relationships of Pogoniinae (Vanilloideae, Orchidaceae): An Herbaceous Example of the Eastern North America-Eastern Asia Phytogeographic Disjunction

rb cL DNA sequences, nuclear ribosomal ITS DNA sequences, morphology, and combined evidence. All these matrices produced patterns that agree on the broader Phylogenetic relationship within the clade. Duckeella is sister to all Pogoniinae, South American species of Cleistes are monophyletic, Pogonia is monophyletic and part of a larger clade of temperate taxa (Isotria, Pogonia, and Cleistes divaricata) from North America and Asia. The structure of the cladograms and the high levels of bootstrap support strongly indicate that the genus Cleistes is paraphyletic. The disjunction between tropical South American and temperate North American taxa as well as the disjunction between Pogonia ophioglossoides in eastern North America with P. minor and P. Japonica in eastern Asia are best explained by speciation following a northward longdistance dispersal and subsequent northwestward migration via Bering land bridges in the Tertiary. This phylogenetic study adds an additional herbaceous example to the growing list of plants that demonstrate this classical biogeographic pattern. Received 5 February 1999/ Accepted in revised form 9 June 1999     

Phylogeny and Biogeography of Thuja L. （Cupressaceae）, an Eastern Asian and North American Disjunct Genus

In order to develop better insights into biogeographic patterns of eastern Asian and North American disjunct plant genera, sequences of nuclear ribosomal DNA internal transcribed spacer (nr DNAITS) region were used to estimate interspecific relationships of Thuja L. (Cupressaceae) and infer its biogeography based on the phylogeny. According to the phylogenetic analysis, two clades were recognized. The first clade included Thuja plicata D. Don (western North America) and T. koraiensis Nakai (northeastern Asia), and the second one contained T. occidentalis (Gord.) Cart. (Japan). The ancestral area of Thuja was inferred to be eastern Asia, and two dispersal events were responsible for the modern distribution of Thuja in North America. Both the North Atlantic land bridge and Bering land bridge were possible routes for the migration of ancestral populations to North America.     

Differential diversifications of South American and Eastern Asian disjunct genera Bocconia and Macleaya (Papaveraceae)

Bocconia (10 species) and Macleaya (2 species) are two disjunct genera between South America and eastern Asia (EAS) in the Papaveraceae offering an opportunity to compare its biogeographic history with that of the well‐known disjunction between EAS and eastern North American (ENA). Our phylogenetic analyses of the chloroplast matK and rbcL gene sequences of Ranunculales including two species of Macleaya and six species of Bocconia supported the monophyly of Bocconia, Macleaya, and Chelidonioideae to which Bocconia and Macleaya belong. Nucleotide sequences of matK, rbcL, and nrDNA ITS supported the sister relationship of Bocconia and Macleaya. Biogeographic analyses of Chelidonioideae using S‐DIVA (statistical dispersal vicariance analysis) and DEC (dispersal extinction cladogenesis) methods inferred Eurasia as the most likely ancestral area of Bocconia and Macleaya and suggested no extinction events in either Bocconia or Macleaya. This agrees with the “Out‐of‐Asia” pattern of the EAS‐ENA disjunction. Molecular dating of Ranunculales with fossil‐based calibrations showed that Bocconia and Macleaya diverged in the late Eocene and early Oligocene, which is much earlier than most EAS‐ENA disjunct taxa. The disjunction may have formed via long distance dispersal or boreotropical connections via the North Atlantic and Bering land bridges. Both Bocconia and Macleaya diversified in the late mid‐Miocene, but Bocconia has apparently experienced a greater diversification probably aided by the evolution of the bird dispersal syndrome in fruit and seed after migration to South America. The greater diversification of Bocconia is also evidenced by the diverse leaf morphology and growth habit in response to colonization in various local habitats in South America.     

Polytrichum tongariroense Colenso,a resurrected name in New Zealand Dendroligotrichum (Polytrichaceae)

Abstract

Interpopulational, interspecific comparison of the habitats, structural features, and distribution of Tomenthypnum in North America and eastern Asia indicate that T. falcifolium and T. nitens are present in both areas. The Chinese populations occur in habitats similar to North American T. falcifolium. Statistical and multivariate analyses of seven characters indicate that the Chinese populations are intermediate with, but distinct from the North American populations of T. nitens and T. falcifolium. We conclude that taxonomically, the Chinese populations belong within the concept of T. falcifolium, and when further collections are known from eastern Asia, may belong to a geographically isolated subspecific taxon.     

Timing the Eastern Asian–Eastern North American Floristic Disjunction: Molecular Clock Corroborates Paleontological Estimates

Sequence data of the chloroplast gene rbcL were used to estimate the time of the well-known eastern Asian–eastern North American floristic disjunction. Sequence divergence of rbcL was examined for 22 species of 11 genera (Campsis, Caulophyllum, Cornus, Decumaria, Liriodendron, Menispermum, Mitchella, Pachysandra, Penthorum, Podophyllum, and Phryma) representing a diverse array of flowering plants occurring disjunctly in eastern Asia and eastern North America. Divergence times of putative disjunct species pairs were estimated from synonymous substitutions, using rbcL molecular clocks calibrated for Cornus. Relative rate tests were performed to assess rate constancy of rbcL evolution among lineages. Corrections of estimates of divergence times for each species pair were made based on rate differences of rbcL between Cornus and other species pairs. Results of these analyses indicate that the time of divergence of species pairs examined ranges from 12.56 ± 4.30 million years to recent (<0.31 million years), with most within the last 10 million years (in the late Miocene and Pliocene). These results suggest that the isolation of most morphologically similar disjunct species in eastern Asia and eastern North America occurred during the global climatic cooling period that took place throughout the late Tertiary and Quaternary. This estimate is closely correlated with paleontological evidence and in agreement with the hypothesis that considers the eastern Asian–eastern North American floristic disjunction to be the result of the range restriction of a once more or less continuously distributed mixed mesophytic forest of the Northern Hemisphere that occurred during the late Tertiary and Quaternary. This implies that in most taxa the disjunction may have resulted from vicariance events. However, long-distance dispersal may explain the disjunct distribution of taxa with low divergence, such as Menispermum.     

Integrated Fossil and Molecular Data Reveal the Biogeographic Diversification of the Eastern Asian-Eastern North American Disjunct Hickory Genus (Carya Nutt.)

The hickory genus (Carya) contains ca. 17 species distributed in subtropical and tropical regions of eastern Asia and subtropical to temperate regions of eastern North America. Previously, the phylogenetic relationships between eastern Asian and eastern North American species of Carya were not fully confirmed even with an extensive sampling, biogeographic and diversification patterns had thus never been investigated in a phylogenetic context. We sampled 17 species of Carya and 15 species representing all other genera of the Juglandaceae as outgroups, with eight nuclear and plastid loci to reconstruct the phylogeny of Carya. The phylogenetic positions of seven extinct genera of the Juglandaceae were inferred using morphological characters and the molecular phylogeny as a backbone constraint. Divergence times within Carya were estimated with relaxed Bayesian dating. Biogeographic analyses were performed in DIVA and LAGRANGE. Diversification rates were inferred by LASER and APE packages. Our results support two major clades within Carya, corresponding to the lineages of eastern Asia and eastern North America. The split between the two disjunct clades is estimated to be 21.58 (95% HPD 11.07-35.51) Ma. Genus-level DIVA and LAGRANGE analyses incorporating both extant and extinct genera of the Juglandaceae suggested that Carya originated in North America, and migrated to Eurasia during the early Tertiary via the North Atlantic land bridge. Fragmentation of the distribution caused by global cooling in the late Tertiary resulted in the current disjunction. The diversification rate of hickories in eastern North America appeared to be higher than that in eastern Asia, which is ascribed to greater ecological opportunities, key morphological innovations, and polyploidy.     

Phylogenomics,biogeography, and evolution of the blue‐ or white‐fruited dogwoods (Cornus)—Insights into morphological and ecological niche divergence following intercontinental geographic isolation

The eastern Asian (EA)–eastern North American (ENA) floristic disjunction represents a major pattern of phytogeography of the Northern Hemisphere. Despite 20 years of studies dedicated to identification of taxa that display this disjunct pattern, its origin and evolution remain an open question, especially regarding post‐isolation evolution. The blue‐ or white‐fruited dogwoods (BW) are the most species‐rich among the four major clades of Cornus L., consisting of ~35 species divided into three subgenera (subg. Yinquania, subg. Mesomora, and subg. Kraniopsis). The BW group provides an excellent example of the EA–ENA floristic disjunction for biogeographic study due to its diversity distribution centered in eastern Asia and eastern North America, yet its species relationships and delineation have remained poorly understood. In this study, we combined genome‐wide markers from RAD‐seq, morphology, fossils, and climate data to understand species relationships, biogeographic history, and ecological niche and morphological evolution. Our phylogenomic analyses with RAxML and MrBayes recovered a strongly supported and well‐resolved phylogeny of the BW group with three intercontinental disjunct clades in EA and ENA or Eurasia and North America, of which two are newly identified within subg. Kraniopsis. These analyses also recovered a potential new species but failed to resolve relationships within the C. hemsleyi–C. schindleri complex. In an effort to develop an approach to reduce computation time, analysis of different nodal age settings in treePL suggests setting a node's minimum age constraint to the lower bound of a fossil's age range to obtain similar ages to that of BEAST. Divergence time analyses with BEAST and treePL dated the BW stem back to the very Late Cretaceous and the divergence of the three subgenera in the Paleogene. By integrating fossil ages and morphology, a total evidence‐based dating approach was used in conjunction with time‐slice probabilities of dispersal under a DEC model to resolve ancestral ranges of each disjunct in the Miocene: Eurasia and ENA (disjunct 1), EA and western North America (disjunct 2), and EA (disjunct 3). The dated biogeographic history supports dispersal via the North Atlantic Land Bridge in the late Paleogene in disjunct 1 and dispersal via the Bering Land Bridge in the Miocene for disjuncts 2 and 3. Character mapping with a stochastic model in phytools and comparison of ecological niche, morphospace, and rate of evolution indicated differential divergence patterns in morphology, ecological niche, and molecules between disjunct sisters. Although morphological stasis was observed in most of the characters, evolutionary changes in growth habit and some features of leaf, flower, and fruit morphology occurred in one or both sister clades. A significant differentiation of ecological habitats in temperature, precipitation, and elevation between disjunct sisters was observed, suggesting a role of niche divergence in morphological evolution post‐isolation. The patterns of evolutionary rate between morphology and molecules varied among disjunct clades and were not always congruent between morphology and molecules, suggesting cases of non‐neutral morphological evolution driven by ecological selection. Our phylogenetic evidence and comparisons of evolutionary rate among disjunct lineages lend new insights into the formation of the diversity anomaly between EA and ENA, with particular support of an early diversification in EA. These findings, in conjunction with previous studies, again suggest that the EA–ENA disjunct floras are an assembly of lineages descended from the Mesophytic Forests that evolved from the early Paleogene “boreotropical flora” through varied evolutionary pathways across lineages.     

Phylogeny and biogeography of Aralia sect. Aralia (Araliaceae)

Aralia sect. Aralia (Araliaceae) consists of approximately eight species disjunctly distributed in Asia and North America. Phylogenetic and biogeographic analyses were conducted using sequences of the internal transcribed spacer regions of the nuclear ribosomal DNA. Aralia racemosa from eastern North America was sister to A. californica from western North America. Aralia cordata from eastern Asia did not form a species-pair relationship with the eastern North American A. racemosa. The two subspecies of A. racemosa formed a monophyletic group. Biogeographic analyses showed a close area relationship between eastern North America and western North America. The Himalayas were cladistically basal and eastern Asia was placed between the Himalayas and North America. The biogeographic analysis supported the origin of the eastern Asian and eastern North American disjunct pattern in Aralia sect. Aralia via the Bering land bridges. Comparisons with results of phylogenetic analyses of other genera suggested that (1) the floristic connection between eastern North America and western North America may be stronger than previously thought; and (2) the biogeographic patterns in the Northern Hemisphere are complex. Furthermore, a lack of correlation between sequence divergence values and phylogenetic positions was observed, suggesting the importance of a phylogenetic framework in biogeographic analyses.     

Evolution of the Eastern Asian and Eastern North American disjunct genus Symplocarpus (Araceae): insights from chloroplast DNA restriction site data

Chloroplast DNA (cpDNA) variation was surveyed with 20 restriction endonucleases for the eastern Asian and eastern North American disjunct genus Symplocarpus (Araceae). The cpDNA phylogeny reveals a sister group relationship between S. foetidus from eastern North America and S. renifolius from eastern Asia. The cpDNA divergence between the two intercontinental sister species is 0.61%, which suggests an estimated divergence time of 6.1 million years ago during the late Miocene. The Bering land bridge hypothesis is compatible with the estimated time of divergence for the migration of Symplocarpus between eastern Asia and North America. Furthermore, a single origin of the exothermic spadices in Symplocarpus is suggested by the phylogeny. The cpDNA data also provide independent support for the recognition of three species within the genus.