The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9–14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.

No abstract

Abstract. Specialists studying the genus Viola have consistently allied the Hawaiian violets comprising section Nosphinium-most of which are subshrubs or treelets-with putatively primitive subshrubs in certain South American violet groups. Hawaiian violets also possess inflorescences, a floral disposition otherwise found only in other genera of the Violaceae, thus strengthening the hypothesis of a very ancient origin for the Hawaiian species. A survey of phylogenetic relationships among infrageneric groups of Viola worldwide using nuclear rDNA internal transcribed spacer (ITS) sequences revealed a dramatically different biogeographic origin for the Hawaiian violets: A monophyletic Hawaiian clade was placed in a close sister relationship with the amphi-Beringian tundra violet, V. langsdorffii s. l., in a highly derived position. This remarkable and unforeseen relationship received strong clade support values across analyses, and monophyly of the Hawaiian lineage was further indicated by a unique 26-base-pair deletion in section Nosphinium. The high polyploid base chromosome number (n Ӎ 40) in the Hawaiian violets relates them to Alaskan and eastern Siberian populations in the polyploid V. langsdorffii complex. More than 50 species of the 260 allochthonous birds wintering in the Hawaiian Islands are found to breed in the Arctic, occupying habitats in which individual birds might have encountered ancestral V. langsdorffii populations and served as dispersers to the central Pacific region. Acquisition of derived morphological traits (e.g., arborescence and inflorescences), significance of a confirmed Arctic origin for a component of the Hawaiian flora, and the likelihood of other ''cryptic'' Arctic elements in the Hawaiian flora deserving independent molecular phylogenetic corroboration are discussed. Extraordinary geographic isolation of the Hawaiian archipelago (more than 3500 km from the nearest continent), a diverse flora of nearly 1000 native angiosperm and approximately 180 pteridophyte species, and an unparalleled 86% endemism in angiosperms and about 70% in pteridophytes (Wagner et al. 1990;Sakai et al. 1995;Wagner and Funk 1995) make the Hawaiian flora one of the most tantalizing foci for evolutionary inquiry. Earlier explicit inferences on the minimum number of successful colonizations responsible for the modern-day Hawaiian vascular flora (Fosberg 1948;Carlquist 1970) have recently been updated to 291 putative events for angiosperms and an additional 115 for pteridophytes (Wagner 1991;Sakai et al. 1995). The Hawaiian flora thus offers unique opportunities for biogeographic and evolutionary studies of oceanic island systems (Carlquist 1965(Carlquist , 1974Wagner and Funk 1995;Givnish 1998). Comprehensive higher-level phylogenetic studies including endemic Hawaiian plants have the potential to elucidate the biogeographic origins of those plant groups and reevaluate previous hypotheses of dispersal and character evolution. Well-established geologic dates pinpoint the time of origin of islands that formed ''c...

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences.A study was conducted using molecular-based population genetic data to interpret biogeographic relationships and survey genetic similarity within and among populations of Alliaria petiolata from its native and introduced ranges. Three of the populations examined were from Europe, the native range of A. petiolata, whereas eight populations were from North America, where A. petiolata was introduced over 125 yr ago and where it has since become an invasive pest. Inter-simple sequence repeat (ISSR) analysis using two different primers revealed 56 unique fragments. Genetic variation was greater in some native populations (Scottish and Dutch) compared with introduced populations. Estimates of the Shannon phenotypic diversity index among populations ranged from 0.917 to 0.996. Analysis of molecular variance indicated that there was strong population structuring, with the greatest variance among populations (61.0%) and with much less variance both between continents (16.3%) and within populations (22.7%). Significant differences were detected within and among populations and between ranges (native and introduced). Unweighted pair-group mean analysis and principal-coordinates analysis separated individuals into two large groups comprising two European populations (Belgium and The Netherlands), on the one hand, and the remaining nine populations, including Scotland, on the other. The data indicate that several North American populations, including those from Ohio, West Virginia, New York, and Kentucky, may have originated from plants from the British Isles, although it is possible that multiple introductions of A. petiolata from Europe have occurred.

Chromosome pairing relationships within cultivated potato (Solanum tuberosum) and its wild tuber-bearing relatives (Solanum sect. Petota) have been interpreted by genome formulas, developed in the early 1900s, through techniques of classic meiotic analysis of interspecifi c hybrids. Here we reexamine potato genome hypotheses with the fi rst phylogenetic analysis of all major genomes of sect. Petota using cloned DNA sequences of the single-copy nuclear gene GBSSI (waxy). Our results provide the fi rst molecular confi rmation of allopolyploidy in wild potato. They both support prior hypotheses and identify novel genome origins never before proposed. The data will be useful to help design crossing strategies to incorporate wild species germplasm into cultivated potato.The cultivated potato, Solanum tuberosum, has about 190 wild species tuber-bearing relatives, forming a well-defi ned phylogenetic group, Solanum sect. Petota (Spooner and Salas, 2006). Th e wild species represent diverse gene pools that are of great importance in breeding resistant and heterotic genotypes. However, not more than 10% of them are currently involved in the breeding process (Ross, 1986). A better understanding of their genome relationships would clarify the prospects for introgression of alien genes into potato and will help in planning eff ective breeding programs.About 70% of these wild species are diploid at 2n = 2x = 24, with the remaining species polyploid, mostly at the tetraploid (2n = 4x = 48) or hexaploid (2n = 6x = 72) levels.