Phylogeny of the New World diploid cottons (Gossypium L., Malvaceae) based on sequences of three low-copy nuclear genes

American diploid cottons (Gossypium L., subgenus Houzingenia Fryxell) form a monophyletic group of 13 species distributed mainly in western Mexico, extending into Arizona, Baja California, and with one disjunct species each in the Galapagos Islands and Peru. Prior phylogenetic analyses based on an alcohol dehydrogenase gene (AdhA) and nuclear ribosomal DNA indicated the need for additional data from other molecular markers to resolve phylogenetic relationships within this subgenus. Toward this end, we sequenced three nuclear genes, the anonymous locus A1341, an alcohol dehydrogenase gene (AdhC), and a cellulose synthase gene (CesA1b). Independent and combined analyses resolved clades that are congruent with current taxonomy and previous phylogenies. Our analyses diagnose at least two long distance dispersal events from the Mexican mainland to Baja California, following a rapid radiation of the primary lineages early in the diversification of the subgenus. Molecular data support the proposed recognition of a new species closely related to Gossypium laxum that was recently collected in Mexico.     

The biogeography of Gunnera L.: vicariance and dispersal

Aim The genus Gunnera is distributed in South America, Africa and the Australasian region, a few species reaching Hawaii and southern Mexico in the North. A cladogram was used to (1) discuss the biogeography of Gunnera and (2) subsequently compare this biogeographical pattern with the geological history of continents and the patterns reported for other Southern Hemisphere organisms. Location Africa, northern South America, southern South America, Tasmania, New Zealand, New Guinea/Malaya, Hawaii, North America, Antarctica. Methods A phylogenetic analysis of twenty‐six species of Gunnera combining morphological characters and new as well as published sequences of the ITS region, rbcL and the rps16 intron, was used to interpret the biogeographical patterns in Gunnera. Vicariance was applied in the first place and dispersal was only assumed as a second best explanation. Results The Uruguayan/Brazilian Gunnera herteri Osten (subgenus Ostenigunnera Mattfeld) is sister to the rest of the genus, followed sequentially upwards by the African G. perpensa L. (subgenus Gunnera), in turn sister to all other, American and Australasian, species. These are divided into two clades, one containing American/Hawaiian species, the other containing all Australasian species. Within the Australasian clade, G. macrophylla Blume (subgenus Pseudogunnera Schindler), occurring in New Guinea and Malaya, is sister to a clade including the species from New Zealand and Tasmania (subgenus Milligania Schindler). The southern South American subgenus Misandra Schindler is sister to a clade containing the remaining American, as well as the Hawaiian species (subgenus Panke Schindler). Within subgenus Panke, G. mexicana Brandegee, the only North American species in the genus, is sister to a clade wherein the Hawaiian species are basal to all south and central American taxa. Main conclusions According to the cladogram, South America appears in two places, suggesting an historical explanation for northern South America to be separate from southern South America. Following a well‐known biogeographical pattern of vicariance, Africa is the sister area to the combined southern South America/Australasian clade. Within the Australasian clade, New Zealand is more closely related to New Guinea/Malaya than to southern South America, a pattern found in other plant cladograms, contradictory to some of the patterns supported by animal clades and by the geological hypothesis, respectively. The position of the Tasmanian G. cordifolia, nested within the New Zealand clade indicates dispersal of this species to Tasmania. The position of G. mexicana, the only North American species, as sister to the remaining species of subgenus Panke together with the subsequent sister relation between Hawaii and southern South America, may reflect a North American origin of Panke and a recolonization of South America from the north. This is in agreement with the early North American fossil record of Gunnera and the apparent young age of the South American clade.     

A revision of the desert shrub Fagonia (Zygophyllaceae)

The taxonomy of the desert shrub genus Fagonia is revised in detail. In total 167 names are accounted for, lectotypes are selected for 33 names, and two names are neotypified. A key to the 34 species is presented, as well as distribution maps for each species. Three new species are described and illustrated, F. densispina and F. latistipulata from Somalia, and F. hadramautica from Yemen. Of the accepted species, 24 are restricted to the Old World and eight to the New World. Most of the Old World species are confined to the Saharo‐Sindian region, with two extending to parts of Macaronesia. Eight species are endemic to the Somali‐Masai region, and two are restricted to southern Africa. In the New World four species are endemic to Baja California, two to northern Baja California and adjacent parts of southwestern USA, one to the province of Coahuila in northeastern Mexico, and one to Chile and Peru. The names of all four species of Fagonia currently on the IUCN Red List of Threatened Plants are put into synonymy.     

A CHLOROPLAST-DNA PHYLOGENY OF THE WILD PERENNIAL RELATIVES OF SOYBEAN (GLYCINE SUBGENUS GLYCINE): CONGRUENCE WITH MORPHOLOGICAL AND CROSSING GROUPS

Hypotheses of evolutionary relationships among the Australian wild perennial relatives of soybean (Glycine subgenus Glycine) are based largely on patterns of meiotic pairing in intra- and interspecific experimental hybrids. This evidence has indicated a number of genome groupings within the subgenus but has not resolved most phylogenetic relationships. Restriction-endonuclease site variation of chloroplast DNA (cpDNA) within the perennial subgenus is reported here, representing a sampling of approximately 3% of the approximately 150-kilobase plastome. Seven hundred twenty-one unique restriction sites were compared within Glycine using 29 restriction endonucleases; 157 sites varied within the genus. Distance and parsimony methods using these data yielded congruent results, recognizing the existence of three major groups within subgenus Glycine: the species-rich and geographically diverse A clade consisting of G. canescens and related taxa; the B clade, which includes the stoloniferous species; and the C group, containing two species with distinctive curved pods. These results are in general agreement with hypotheses based on genome analysis; inconsistencies involve the inclusion of genetically divergent taxa such as G. falcata in well-supported plastome clades comprised of otherwise interfertile species. Such findings are not unexpected if crossing barriers are considered to be unique features of such anomalous species, paralleling their often numerous morphological and cpDNA autapomorphies. Consideration of cpDNA divergence within the three major clades of subgenus Glycine indicates that the rate of plastome evolution is uncoupled from rates of morphological or ecological diversification.     

Chloroplast DNA variation in diploid and polyploid species of Bromus (Poaceae) subgenera Festucaria and Ceratochloa

Summary Chloroplast DNA (cpDNA) restriction endonuclease patterns are used to examine phylogenetic relationships between Bromus subgenera Festucaria and Ceratochloa. Festucaria is considered monophyletic based on the L genome, while Ceratochloa encompasses two species complexes: the B. catharticus complex, which evolved by combining three different genomes, and the B. carinatus complex, which is thought to have originated from hybridization between polyploid species of B. catharticus and diploid members of Festucaria. All species of subgenus Ceratochloa (hexaploids and octoploids) were identical in chloroplast DNA sequences. Similarly, polyploid species of subgenus Festucaria, except for B. auleticus, were identical in cpDNA sequences. In contrast, diploid species of subgenus Festucaria showed various degrees of nucleotide sequence divergence. Species of subgenus Ceratochloa appeared monophyletic and phylogenetically closely related to the diploid B. anomalus and B. auleticus of subgenus Festucaria. The remaining diploid and polyploid species of subgenus Festucaria appeared in a distinct grouping. The study suggests that the B. catharticus complex must have been the maternal parent in the proposed hybrid origin of B. carinatus complex. Although there is no direct evidence for the paternal parent of the latter complex, the cpDNA study shows the complex to be phylogenetically very related to the diploid B. anomalus of subgenus Festucaria.     

Multiple nuclear genes stabilize the phylogenetic backbone of the genus Quercus

Phylogenetic relationships among 108 oak species (genus Quercus L.) were inferred using DNA sequences of six nuclear genes selected from the existing genomic resources of the genus. Previous phylogenetic reconstructions based on traditional molecular markers are inconclusive at the deeper nodes. Overall, weak phylogenetic signals were obtained for each individual gene analysis, but stronger signals were obtained when gene sequences were concatenated. Our data support the recognition of six major intrageneric groups Cyclobalanopsis, Cerris, Ilex, Quercus, Lobatae and Protobalanus. Our analyses provide resolution at deeper nodes but with moderate support and a more robust infrageneric classification within the two major clades, the ‘Old World Oaks’ (Cyclobalanopsis, Cerris, Ilex) and ‘New World Oaks’ (Quercus, Lobatae, Protobalanus). However, depending on outgroup choice, our analysis yielded two alternative placements of the Cyclobalanopsis clade within the genus Quercus. When Castanea Mill. was chosen as outgroup, our data suggested that the genus Quercus comprised two clades corresponding to two subgenera as traditionally recognized by Camus: subgenus Euquercus Hickel and Camus and subgenus Cyclobalanopsis Øersted (Schneider). However, when Notholithocarpus Manos, Cannon and S. Oh was chosen as an outgroup subgenus Cyclobalanopsis clustered with Cerris and Ilex groups to form the Old World clade. To assess the placement of the root, we complemented our dataset with published data of ITS and CRC sequences. Based on the concatenated eight gene sequences, the most likely root position is at the split between the ‘Old World Oaks’ and the ‘New World Oaks’, which is one of the alternative positions suggested by our six gene analysis. Using a dating approach, we inferred an Eocene age for the primary divergences in Quercus and a root age of about 50–55 Ma, which agrees with palaeobotanical evidence. Finally, irrespective of the outgroup choice, our data boost the topology within the New World clade, where (Protobalanus + Quercus) is a sister clade of Lobatae. Inferred divergence ages within this clade and the Cerris–Ilex clade are generally younger than could be expected from the fossil record, indicating that morphological differentiation pre-dates genetic isolation in this clade.     

The bumblebees of the subgenus Subterraneobombus: integrating evidence from morphology and DNA barcodes (Hymenoptera,Apidae, Bombus)

Although bumblebees have received a lot of attention, some taxonomic problems have persisted for many years. One particularly obdurate case has been the species of the subgenus Subterraneobombus. We revise the bees of this subgenus by integrating evidence from both morphology and, for a 5% subsample, from DNA (cytochrome c oxidase subunit 1, CO1) barcodes from pinned museum specimens. We apply a reciprocal illumination procedure: (1) taxa recognized previously from morphology are used to stratify samples for DNA subsampling; (2) DNA barcodes from these subsamples are used to recognize groups of phylogenetically related specimens; and (3) for these groups, we re‐examine morphological characters in order to recognize and diagnose species. A total of 3854 specimens from 1535 samples from across the geographic range of the subgenus throughout the Holarctic and northern Oriental regions are identified to 11 species. This includes one species newly recognized from Mongolia, Bombus mongolensis Williams sp. nov. Taxon concepts are modified substantially for four species, seven lectotypes are designated, and four new synonyms are recognized. The prevailing usage of Bombus distinguendus is maintained as valid by designating Bombus elegans as a nomen oblitum and designating B. distinguendus as a nomen protectum. Identification keys and colour‐pattern diagrams are provided, and geographic distributions, elevational ranges, and phenological activity periods are described to characterize the species. An estimate of the biogeographic history is reconstructed with dispersal–vicariance analysis. In this study, DNA barcode data have been a cost‐effective source of additional characters for diagnosing groups of specimens. The barcode data contributed directly to recognizing the one new species, of which females remain difficult to identify from morphology alone. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 813–862.     

Repeated range expansion and niche shift in a volcanic hotspot archipelago: Radiation of C4 Hawaiian Euphorbia subgenus Chamaesyce (Euphorbiaceae)

Woody perennial plants on islands have repeatedly evolved from herbaceous mainland ancestors. Although the majority of species in Euphorbia subgenus Chamaesyce section Anisophyllum (Euphorbiaceae) are small and herbaceous, a clade of 16 woody species diversified on the Hawaiian Islands. They are found in a broad range of habitats, including the only known C₄ plants adapted to wet forest understories. We investigate the history of island colonization and habitat shift in this group. We sampled 153 individuals in 15 of the 16 native species of Hawaiian Euphorbia on six major Hawaiian Islands, plus 11 New World close relatives, to elucidate the biogeographic movement of this lineage within the Hawaiian island chain. We used a concatenated chloroplast DNA data set of more than eight kilobases in aligned length and applied maximum likelihood and Bayesian inference for phylogenetic reconstruction. Age and phylogeographic patterns were co‐estimated using BEAST. In addition, we used nuclear ribosomal ITS and the low‐copy genes LEAFY and G3pdhC to investigate the reticulate relationships within this radiation. Hawaiian Euphorbia first arrived on Kaua`i or Ni`ihau ca. 5 million years ago and subsequently diverged into 16 named species with extensive reticulation. During this process Hawaiian Euphorbia dispersed from older to younger islands through open vegetation that is disturbance‐prone. Species that occur under closed vegetation evolved in situ from open vegetation of the same island and are only found on the two oldest islands of Kaua`i and O`ahu. The biogeographic history of Hawaiian Euphorbia supports a progression rule with within‐island shifts from open to closed vegetation.     

Multilocus phylogeny and taxonomy of pikas of the subgenus Ochotona (Lagomorpha,Ochotonidae)

A complete set of pika taxa, belonging to the subgenus Ochotona, was studied using craniometric and multilocus genetic analyses. We examined 1,007 skulls, covering the entire distribution range of the subgenus, as well as the mitochondrial COI gene and three nuclear introns in 31 specimens, representing nearly all taxa in question. An additional set of 167 COI gene sequences and 357 cytb gene sequences was analysed to enlarge the geographical extent of genetic data and to compare the results with previous publications. We found that the subgenus consists of eight species. One of them, Ochotona morosa, is elevated to the full species rank for the first time. The name of this species is given preliminarily and should be studied additionally. Several cases of interspecies hybridisation were found, which indicates that mitochondrial DNA cannot be used for species identification in this subgenus. Taxon Ochotona qionglaiensis, which was recently described as a separate species, represents a relic mitochondrial lineage of Ochotona thibetana. Another recently described species, Ochotona yarlungensis, is a Nubra pika with its native mitochondrial DNA, firstly found for this species. Intraspecies variation was analysed for several species for the first time. Thus, new subspecies (Ochotona thibetana fengii ssp. n.) was found within O. thibetana.     

Review of the Central American Species of the Subgenus Quedionuchus of the Genus Quedius (Col. Staphylinidae)

All species of the subgenus Quedionuchus Shp. of the genus Quedius Steph. (Staphylinidae), known to occur at present in Central America are treated. A key is given. Seven species are described as new: Q. ollin (Mexico), tecpatl (Mexico), cipactli (Guatemala), xochitl (Mexico), ehecatl (Mexico), calli (Mexico) and coatl (Mexico). Lectotypes are designated for the following 4 species: nigerrimus (Shp.), angustus (Shp.), femoralis (Shp.) and spinipes (Shp.). The species are described and illustrated, and the known data on their bionomics and geographical distribution are given.     

A multi‐locus approach resolves the phylogenetic relationships of the Simulium asakoae and Simulium ceylonicum species groups in Malaysia: evidence for distinct evolutionary lineages

A multi‐locus approach was used to examine the DNA sequences of 10 nominal species of blackfly in the Simulium subgenus Gomphostilbia (Diptera: Simuliidae) in Malaysia. Molecular data were acquired from partial DNA sequences of the mitochondria‐encoded cytochrome c oxidase subunit I (COI), 12S rRNA and 16S rRNA genes, and the nuclear‐encoded 18S rRNA and 28S rRNA genes. No single gene, nor the concatenated gene set, resolved all species or all relationships. However, all morphologically established species were supported by at least one gene. The multi‐locus sequence analysis revealed two distinct evolutionary lineages, conforming to the morphotaxonomically recognized Simulium asakoae and Simulium ceylonicum species groups.     

Phylogenetic relationships in Peniocereus (Cactaceae) inferred from plastid DNA sequence data

The phylogenetic relationships of Peniocereus (Cactaceae) species were studied using parsimony analyses of DNA sequence data. The plastid rpl16 and trnL-F regions were sequenced for 98 taxa including 17 species of Peniocereus, representatives from all genera of tribe Pachycereeae, four genera of tribe Hylocereeae, as well as from three additional outgroup genera of tribes Calymmantheae, Notocacteae, and Trichocereeae. Phylogenetic analyses support neither the monophyly of Peniocereus as currently circumscribed, nor the monophyly of tribe Pachycereeae since species of Peniocereus subgenus Pseudoacanthocereus are embedded within tribe Hylocereeae. Furthermore, these results show that the eight species of Peniocereus subgenus Peniocereus (Peniocereus sensu stricto) form a well-supported clade within subtribe Pachycereinae; P. serpentinus is also a member of this subtribe, but is sister to Bergerocactus. Moreover, Nyctocereus should be resurrected as a monotypic genus. Species of Peniocereus subgenus Pseudoacanthocereus are positioned among species of Acanthocereus within tribe Hylocereeae, indicating that they may be better classified within that genus. A number of morphological and anatomical characters, especially related to the presence or absence of dimorphic branches, are discussed to support these relationships.     

Molecular identification of cryptic bumblebee species from degraded samples using PCR–RFLP approach

The worldwide decline and local extinctions of bumblebees have raised a need for fast and accurate tools for species identification. Morphological characters are often not sufficient, and molecular methods have been increasingly used for reliable identification of bumblebee species. Molecular methods often require high‐quality DNA which makes them less suitable for analysis of low‐quality or older samples. We modified the PCR–RFLP protocol for an efficient and cost‐effective identification of four bumblebee species in the subgenus Bombus s. str. (B. lucorum, B. terrestris, B. magnus and B. cryptarum). We used a short partial mitochondrial COI fragment (446 bp) and three diagnostic restriction enzymes (Hinf I, Hinc II and Hae III) to identify species from degraded DNA material. This approach allowed us to efficiently determine the correct species from all degraded DNA samples, while only a subset of samples 64.6% (31 of 48) resulted in successful amplification of a longer COI fragment (1064 bp) using the previously described method. This protocol can be applied for conservation and management of bumblebees within this subgenus and is especially useful for fast species identification from degraded samples.     

Molecular phylogeny of black flies (Diptera: Simuliidae) from Thailand, using ITS2 rDNA

The sequences of the second internal transcribed spacer (ITS2) of ribosomal DNA (rDNA) were determined for 40 black fly species from Thailand, belonging to 4 subgenera of the genus Simulium, namely Gomphostilbia (12 species), Nevermannia (5 species), Montisimulium (1 species), Simulium sensu stricto (21 species), and an unknown subgenus with one species (Simulium baimaii). The length of the ITS2 ranged from 247 to 308 bp. All black fly species had high AT content, ranging from 71 to 83.8%. Intraindividual variation (clonal variation) occurred in 13 species, ranging from 0.3 to 1.1%. Large intrapopulation and interpopulation heterogeneities exist in S. feuerboni from the same and different locations in Doi Inthanon National Park, northern Thailand. Phylogenetic relationships among 40 black fly species were examined using PAUP (version 4.0b10) and MrBAYS (version 3.0B4). The topology of the trees revealed two major monophyletic clades. The subgenus Simulium and Simulium baimaii were placed in the first monophyletic clade, whereas the subgenera Nevermannia + Montisimulium were placed as the sister group to the subgenus Gomphostilbia in the second monophyletic clade. Our results suggest that S. baimaii belongs to the malyschevi-group or variegatum-group in the subgenus Simulium. The molecular phylogeny generally agrees with existing morphology-based phylogenies.     

Phylogenetics and taxonomy of the New World leafy spurges,Euphorbia section Tithymalus (Euphorbiaceae)

The 480 species of leafy spurges, Euphorbia subgenus Esula, represent the main temperate radiation in the large genus Euphorbia. This group is distributed primarily in temperate Eurasia, but with smaller, disjunct centres of diversity in the mountains of the Old World tropics, in temperate southern Africa and in the New World. The majority of New World diversity (32 species) occurs in a single section, section Tithymalus. We analysed sequences of the nrITS and plastid ndhF, trnH‐psbA, trnS‐trnG and trnD‐trnT regions to reconstruct the phylogeny of section Tithymalus and to examine the origins and diversification of the species native to the New World. Our results indicate that the New World species of section Tithymalus form a clade that is sister to the widespread, weedy E. peplus. The New World species fall into two primary groups: a ‘northern annual clade’ from eastern North America and a diverse clade of both annual and perennial species that is divided into three subgroups. Within the second group, there is a small ‘southern annual clade’ from Texas and northern Mexico, a perennial ‘Brachycera clade’ from the western United States and northern Mexico, and a perennial ‘Esuliformis clade’ from montane areas of Mexico, Guatemala, Honduras and the Caribbean island of Hispaniola. Ancestral state reconstructions indicate that the annual habit probably evolved in the ancestor of E. peplus and the New World clade, with a subsequent reversal to the perennial habit. In conjunction with this phylogenetic framework, the New World species of section Tithymalus are comprehensively reviewed. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 191–228.     

Phylogeny of bumble bees in the New World subgenus Fervidobombus (Hymenoptera: Apidae): congruence of molecular and morphological data

We present new DNA sequence data (12S, 16S, and opsin gene fragments) and morphological characters of the male genitalia for a phylogenetic analysis of the bumble bee subgenus Fervidobombus. There is no significant incongruence between the three molecular data sets, and little incongruence between the DNA and morphology. Simultaneous analysis of all the data partitions resulted in a tree that was entirely congruent with the All-DNA tree. Optimization of the geographic locations of the taxa onto the tree topology using dispersal/vicariance analysis suggests a complex picture of spread and diversification of Fervidobombus from the Old World into the southern New World. There is a phylogenetic component to their spread into tropical rain forest, as the two primary rain forest species (Bombus transversalis and Bombus pullatus) comprise a monophyletic clade, along with a third species, Bombus atratus, which is widely distributed in South America, including lowland subtropical habitats.     

Phylogenetic relationships of Sargassum (Sargassaceae, Phaeophyceae) with reference to a taxonomic revision of the section Phyllocystae based on ITS-2 nrDNA sequences

Sequences of the end of the 5.8S gene and the internal transcribed spacer 2 (ITS‐2) of nuclear ribosomal DNA have been determined for 19 species of the brown algal genus Sargassum (Sargassaceae), representing three subgenera and eight sections (sections are in parentheses): Phyllotrichia, Bactrophycus (Teretia, Spongocarpus, Halochloa and Repentia) and Sargassum (Acanthocarpicae, Malacocarpicae, Zygocarpicae) to assess the taxonomic position of the section Phyllocystae traditionally included within the Bactrophycus. The sequence of Myagropsis myagroides (Mertens ex Turner) Fensholt (Sargassaceae) was used as an outgroup. Sequences of ITS‐2 were analyzed using neighbor‐joining, parsimony and maximum likelihood methods. The results showed the existence of three clades in Sargassum, corresponding to the three subgenera. The subgenus Phyllotrichia is positioned near the outgroup. Two robust clades were obtained, one corresponding to the subgenus Bactrophycus and the other to the subgenus Sargassum. Sargassum mcclurei Setchell and Sargassum quinhonense Nguyen, the two Phyllocystae investigated, are close to species belonging to the section Zygocarpicae in the subgenus Sargassum. A transfer of the section Phyllocystae to the subgenus Sargassum is therefore proposed on the basis of molecular data (ITS‐2) and morphological data (receptacles and basal leaf).     

A cladistic study of North AmericanCoreopsis (Asteraceae: Heliantheae)

A cladistic study of all 44 species of North AmericanCoreopsis was performed using 35 characters. The resulting cladogram indicated that all 11 sections are monophyletic. At the intersectional level, two lineages were revealed, one consisting of six sections occurring almost exclusively in Mexico and California, and another comprising five sections restricted largely to the eastern and southeastern United States. The cladogram is similar to phylogenies produced by less explicit methods but it differs in two major respects: the monotypic sect.Silphidium is placed with other sections from the southeastern United States rather than with Mexican sections, and sect.Anathysana from Mexico is more closely allied with the three California sections than with sect.Electra from Mexico.     

THE POLYTYPIC SPECIES REVISITED: GENETIC DIFFERENTIATION AND MOLECULAR PHYLOGENETICS OF THE TIGER SALAMANDER AMBYSTOMA TIGRINUM (AMPHIBIA: CAUDATA) COMPLEX

We present a phylogenetic analysis of the Ambystoma tigrinum complex, based on approximately 840 base pairs of mitochondrial-DNA sequence from the rapidly evolving D-loop and an adjacent intron. Our samples include populations of the continentally distributed species, A. tigrinum, plus all described species of Mexican ambystomatids. Sequence divergence is low, ranging from 0–8.5%, and most phylogenetic groupings are weakly supported statistically. We identified eight reasonably well-defined clades from the United States and Mexico, with the geographically isolated A. californiense from California as the probable sister group to the remaining taxa. Our sequence data are not capable of resolving the relationships among these clades, although the pattern of transitional-site evolution suggests that these eight lineages diverged during a period of rapid cladogenesis. We roughly calibrate a molecular clock and identify a few lineages that significantly deviate from the slow, baseline rate of 0.5–0.75% per million years. Our data also suggest that species boundaries for several U.S. and Mexican species need to be altered and that the concept of a continentally distributed, polytypic tiger salamander is not valid.     

A molecular phylogeny of Arceuthobium (Viscaceae) based on nuclear ribosomal DNA internal transcribed spacer sequences

Ribosomal DNA (rDNA) internal transcribed spacer (ITS) and 5.8S rDNA sequences were obtained from 22 species of dwarf mistletoes (Arceuthobium — Viscaceae) to test phylogenetic relationships. Interspecific distances ranged from 0 to 21.4% between New World species, values two to five times higher than those measures for the ITS region in other plants. One Old World species (A. oxycedri) and one New World species (A. abietis-religiosae) were remarkably similar to each other but exhibited up to 41% sequence divergence from the remaining species. Minimum length trees support the concept of a verticillately branched subgenus Arceuthobium; however, interspecific distances indicate this group is extremely heterogeneous. Subgenus Vaginata, Section Vaginata, is centered in Mexico and encompasses all the taxa previously placed in this group but is expanded to include several species previously classified in Section Campylopoda (e.g., A. divaricatum, A. rubrum, and A. strictum). The sister group relationship between A. divaricatum and A. douglasii, first seen following isozyme analysis, is supported by ITS sequence data. Section Campylopoda s. s. is now composed of 13 mainly U.S. species that show a high degree of morphological and genetic similarity. The eastern dwarf mistletoe, A. pusillum, is not closely related to A. douglasii but rather with A. bicarinatum from Hispaniola, which suggests that these taxa represent highly modified relicts that shared an ancestor in the early Tertiary. Two endemic species from Mexico and Central America (A. guatemalense and A. pendens) formed a sister group and have been placed in a new Section (Penda). Rapid molecular evolution in Arceuthobium may be associated with the adaptive radiation of this genus on numerous conifer hosts.