Polyphyly of the Padus group of Prunus (Rosaceae) and the evolution of biogeographic disjunctions between eastern Asia and eastern North America

Prunus subgenus Padus is a group with a wide distribution in temperate eastern Asia and eastern North America with one species extending to Europe and one to Central America. Phylogenetic relationships of subgenus Padus were reconstructed using sequences of nuclear ribosomal ITS, and plastid ndhF gene, and rps16 intron and rpl16 intron. Prunus subgenus Padus is shown to be polyphyletic. Taxa of subgenus Padus and subgenus Laurocerasus are highly intermixed in both the ITS and the plastid trees. The results support two disjunctions between eastern North America and Eurasia within the Padus group. One disjunction is between Prunus virginiana of eastern North America and P. padus of Eurasia, estimated to have diverged at 2.99 (95 % HPD 0.59–6.15)–4.1 (95 % HPD 0.63–8.59) mya. The other disjunction is between P. serotina and its Asian relatives. The second disjunction may have occurred earlier than the former one, but the age estimate is difficult due to the unresolved phylogenetic position of the P. serotina complex.     

Evolution of biogeographic disjunction between eastern Asia and eastern North America in Phryma (Phrymaceae)

This study examines molecular and morphological differentiation in Phryma L., which has only one species with a well-known classic intercontinental disjunct distribution between eastern Asia (EA) and eastern North America (ENA). Phylogenetic analysis of nuclear ribosomal ITS and chloroplast rps16 and trnL-F sequences revealed two highly distinct clades corresponding to EA and ENA. The divergence time between the intercontinental populations was estimated to be 3.68 ± 2.25 to 5.23 ± 1.37 million years ago (mya) based on combined chloroplast data using Bayesian and penalized likelihood methods. Phylogeographic and dispersal-vicariance (DIVA) analysis suggest a North American origin of Phryma and its migration into EA via the Bering land bridge. Multivariate analysis based on 23 quantitative morphological characters detected no geographic groups at the intercontinental level. The intercontinental populations of Phryma thus show distinct molecular divergence with little morphological differentiation. The discordance of the molecular and morphological patterns may be explained by morphological stasis due to ecological similarity in both continents. The divergence of Phryma from its close relatives in the Phrymaceae was estimated to be at least 32.32 ± 4.46 to 49.35 ± 3.18 mya.     

Hybridization between escaped domestic and wild American mink (Neovison vison)

The release of domesticated organisms into natural populations may adversely affect these populations through predation, resource competition, and the introduction of disease. Additionally, the potential for hybridization between wild and domestic conspecifics is of great concern because it can alter the evolutionary integrity of the affected populations. Wild American mink ( Neovison vison ) populations may be threatened not only by competition for resources with domestic mink originating from farms, but by breeding with such escapees. Using 10 microsatellite loci, we genotyped mink from Ontario, Canada, sampled from two farms, two putatively mixed populations in regions surrounding the mink farms, and two wild populations with no recent history of mink farming. Using individual-based Bayesian population assignment, we identified four population clusters, including one wild, and three domestic populations. The latter were not clustered by farm but rather by distinct line-bred colour phases. Population clustering also identified domestic and hybrid mink in the free-ranging populations. Nearly two-thirds of the mink sampled in the two putatively mixed populations (78% and 43%) were either farm escapees or descendants of escapees. Principal components analysis of allele frequencies supported our Bayesian assignment results. The power of our assignment test was assessed using simulated hybrid genotypes which suggested that our overall correct classification rate was 96.2%. The overwhelming presence of domestic animals and their hybridization with mink in natural populations is of great concern for the future sustainability of wild mink populations.     

Phylogeny and biogeography of Sassafras (Lauraceae) disjunct between eastern Asia and eastern North America

Sassafras (Lauraceae) consists of three species disjunct between eastern Asia (S. tzumu and S. randaiense) and eastern North America (S. albidum). Phylogenetic analysis based on sequences of nuclear ribosomal ITS and three chloroplast non-coding regions (rpl16, trnL-F, and psbA-trnH) showed that Sassafras is monophyletic and that the eastern North American S. albidum is sister to the clade of its two eastern Asian counterparts. Their intercontinental divergence was estimated to be 13.80 ± 2.29−16.69 ± 2.52 million years ago (mya) using the penalized likelihood method with the ITS and three chloroplast markers. Biogeographic analyses combined with fossil evidence suggest that Sassafras has a relict distribution in the Northern Hemisphere without a Gondwanan link. The divergence time of the two eastern Asian species (the continental Chinese Sassafras tzumu and S. randaiense endemic to Taiwan) is estimated to be 0.61 ± 0.75−2.23 ± 0.76 mya. Sassafras randaiense from Taiwan was most likely derived from an ancestor from continental China.     

Molecular divergence between disjunct taxa in eastern Asia and eastern North America

Eastern Asian-eastern North American disjuncts in four genera were examined for allozyme divergence and sequence divergence of the internal transcribed spacers (ITS) of nuclear ribosomal DNA. The disjunct pairs of taxa include Caulophyllum robustum-C. thalictroid.es, Menispermum dauricum-M. canadense, Penthorum chinense-P. sedoides, and Phryma leptostachya var. asiatica-P. leptostachya var. leptostachya. Allozyme divergence was comparable in Caulophyllum and Penthorum (genetic identities of 0.534 and 0.546) and was considerably higher than between pairs of taxa in Menispermum (0.273) and Phryma (0.291). Caulophyllum and Penthorum, which have the highest genetic identities at allozyme loci, also have low ITS sequence divergences (1.30 and 1.65%, respectively). Phryma, which has low isozyme identity, also has the highest ITS sequence divergence (4.46%). The two taxa of Menispermum have low ITS sequence divergence (0.93%) despite having a low identity (0.273) at allozyme loci. The results suggest that divergence between the taxa in the four genera are not the result of a single historical event. Estimated divergence times are reasonably consistent with a late Miocene disjunction for Caulophyllum and Penthorum, whereas the age of the Phryma disjunction is calculated at over 20 million years. The nonconcordant divergences between allozymes and ITS sequences in Menispermum may be caused by concerted evolution in the latter or possibly longer generation time in the woody plants. Additional molecular data are needed to clarify the situation.     

Revision of Limonium (Plumbaginaceae) in eastern North America

The number of species ofLimonium in eastern North America has long been a matter of taxonomic concern. The complex of six to seven “species” is better treated as a single, highly variable species,Limonium carolinianum (Walter) Britton.     

Diversity and relationships of bradyrhizobia from legumes native to eastern North America

DNA sequencing and polymerase chain reaction (PCR) assays with lineage-specific primers were used to analyze the diversity of 276 isolates of Bradyrhizobium sp. nodule bacteria associated with 13 native legumes species in the northeastern United States, representing eight genera in six legume tribes. A PCR screen with two primer pairs in the rRNA region indicated that seven of the legume species were exclusively associated with strains having markers resembling Bradyrhizobium elkanii, while the remaining six host species harbored strains related to both B. elkanii and Bradyrhizobium japonicum. Sequence analysis of 22 isolates for portions of 16S rRNA and 23S rRNA yielded congruent phylogenetic trees and showed that isolates from different legume genera often shared similar or identical sequences. However, trees inferred from portions of two other genes (alpha-ketoglutarate dioxygenase gene (tfdA), the alpha-subunit of nitrogenase (nifD)) differed significantly from the rRNA phylogeny. Thus, for Bradyrhizobium populations in this region, lateral gene transfer events appear to have altered genealogical relationships of different portions of the genome. These results extend the number of likely cases of gene transfer between divergent taxa of Bradyrhizobium (from members of the B. elkanii lineage to the B. japonicum group) and suggest that transfers have also occurred among separate subgroups of the B. elkanii lineage.     

Revision of Lyonothamnus A. Gray (Rosaceae) from the Neogene of Western North America

Lyonothamnus Gray is a monotypic genus of evergreen trees endemic to California's Channel Islands. There is one species, L. floribundus, with two subspecies, ssp. floribundus and ssp. asplenifolius. Subspecies floribundus has simple and entire-margined leaves, while leaves of ssp. asplenifolius are pinnate and composed of three to seven primary segments. Despite its restricted modern occurrence, three fossil species have been described from Neogene paleofloras in the far western United States. Lyonothamnus mohavensis Axelrod is known from California; L. parvifolius (Axelrod) Wolfe and L. cedrusensis Axelrod, from Nevada. However, the size ranges used to segregate these species were all found to fall within the range of L. parvifolius from Stewart Valley, Nevada. Study of intact leaves reveals that the combination of (1) number of primary segments, (2) length of primary segments, (3) number of medial secondary segments per primary segment, and (4) lengths and widths of medial secondary segments is important in segregating species. Using these characters, L. parvifolius and L. wolfei Erwin et Schorn sp. nov. are recognized from Nevada and Oregon, and two species, L. mohavensis and L. axelrodii Erwin et Schorn sp. nov., from California. This renewed taxonomy within an updated temporal framework provides an important first step toward understanding the evolution, diversity, paleoecology, and paleobiogeographic history of this unusual member of the Rosaceae.     

Hybridization between Fagopyrum (Polygonaceae) species native to China

Thirty-eight crosses between seven Fagopyrum species native to China were studied. Following normal pollination, there were very low inter-group crossabilities (only 0 3%) between five species in the large-achene group and two species (E gracilipes and E pleioramosum) in the small-achene group, and high (15 50%) within the large-achene group, i.e. E esculentum, E tataricum, E zuogongense, E pilus and E megaspartanium. Crosses between various types of (lowers (homostyle, heterostyle etc.) suggested that the intraspecific incompatibility also occurs in interspecific crosses. The hybrid seeds obtained from interspecific crosses all withered or shrivelled and lacked activity. Only one hybrid plant was obtained, tetraploid E esculentum x tetraploid E zuogongense. The hybrid displayed anomalous behaviour at meiosis, pollen grain sterility and withering of achenes, confirming the genetic differences between E esculentum and E zuogongense. The results support the hypothesis that E megaspartanium and E pilus are the possible ancestors of cultivated buckwheat     

Host plants of someRhinanthoideae (Scrophulariaceae) of eastern North America

Twenty three species in 11 genera were examined in the field to determine hosts. OnlyStriga asiatica andSeymeria cassioides have a narrow host range being restricted to grasses and pines, respectively. These are the only species which cause pronounced and sometimes serious host damage. The other species attach to a great diversity of hosts.     

Hybridization studies in the aster occidentalis (Asteraceae) polyploid complex of western North America

Hybridization experiments were carried out with 12 of the approximately 15 species in the complex. The crosses involved plants at various ploidy levels from diploid (n=8) to duodecaploid (n=48). Viable F₁ progeny were obtained from 26% of the crosses involving diploids, and from 66% of the crosses between polyploids. All but a few of the progeny had a high degree of pollen fertility, and all of those examined had regular pairing of chromosomes at meiosis. Even at the diploid level few reproductive barriers isolate the taxa of this complex, although morphologically distinct entities can be recognized.     

Fabaceae (legume) pollen as an anthropogenic indicator in eastern North America

Vegetation History and Archaeobotany - European land-use indicators in North America typically include pollen from Poaceae (grasses), Ambrosia (ragweed), Rumex (dock), and/or Plantago (plantain). A...     

Stomata on the pericarp of species of the genus Rosa L. (Rosaceae)

Achenes of 36 species representing all subgenera and sections of the genus Rosa were studied. All have stomata on the pericarp that seem to be normal in appearance. They are usually few, scattered, mostly on the upper part of fruit, and open or closed. This is the first report of stomata on fruits of Rosa.     

The native subspecies of Juncus effusus (Juncaceae) in western North America

Juncus effusus s. str. has two native representatives on the coast of western North America. A new combination is provided forJuncus effusus subsp.pacificus, ranging from California to British Columbia.Juncus effusus subsp.austrocalifornicus is newly described from southernmost California, Arizona, and Baja California, México. It differs from subsp.pacificus by its pale sheaths, with less thickened and less overlapping margins, and its disjunct distribution. A key is provided for the subspecies ofJ. effusus in North America.     

Two pairs of vicarious species of cypripedium (orchidaceae) from eastern asia and eastern North America

The taxonomy and phytogeography of two pairs of vicarious cypripediums,C. reginae Walt. andC. flavum Hunt & Summerh., andC. arietinum R. Br. andC. plectrochilon Franchet, are discussed. They are all distinct species, though there exist close relationships between the members of each pair. Of phytogeographic interest are the strong resemblance of distribution patterns of these two pairs of vicarious species, the similarity of their habitats, and the fact that all are rather primitive members in the genus.     

The region effect on mesoscale plant species richness between eastern Asia and eastern North America

The greater number of plant species in temperate eastern Asia compared to eastern North America has been ascribed to both local environment and regional characteristics, but the relative contributions of each have not been resolved. In this analysis, we related species richness of flowering plants in mesoscale floras (<10⁴ km²) dominated by temperate forest vegetation to area, elevation, latitude, and several climate variables. When analyses were conducted separately within each region, area and, in eastern Asia, elevation, were the primary determinants of species richness. It appears that the number of species in mesic temperate floras within these regions is largely unrelated to the relatively narrow range of local climate factors associated with these floras. Analysis of covariance of the logarithm of species richness with the logarithm of area (b=0.148) and climate measurements as independent variables revealed a region effect, with species richness in eastern Asia exceeding that in eastern North America by 0.294 log₁₀ units, or a factor of 2.0. Similar regional differences in species richness were apparent in floras compiled from larger areas. Understanding differences in plant species richness between regions requires consideration of regional influences, whose effects should be tested in comparative analyses based on floristic surveys of ecologically characterized small areas.