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  • 1
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Peroxidase phenotypes of two all-agamospermous “species” of Eupatorium in the southeastern United States were examined. The result supported a hybrid origin (E. recurvans × E. rotundifolium) for E. scabidum and an autopolyploid origin from E. recurvans for E. mohrii. Notable variations of E. scabridum in its leaf morphology and peroxidase phenotype were suggestive of occasional sexuality in this agamospermous “species”.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Melbourne, Australia : Blackwell Science Pty
    Plant species biology 16 (2001), S. 0 
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Cytogeographical studies have revealed the distribution of sexual diploids and agamospermous polyploids of Stevia ovata and four related species: Stevia nepetifolia, Stevia oligophylla, Stevia origanoides and Stevia triflora in Mexico. These species are distributed mainly in the temperate and subhumid montane region. Agamospermous triploids are the forms most abundantly and widely distributed geographically in each of the five species. Diploids occur in low frequencies except in S. origanoides. For the five species, diploids are restricted mainly to the temperate montane ranges of the south-western Pacific side of Mexico, but they also occur sporadically in the relatively isolated areas from Oaxaca to Durango, Mexico D. F. and Nuevo Leon. Although the distribution of the temperate forests must have moved southward and northward following climatic fluctuations, even in the lower latitudes of Mexico, the largely stable temperate vegetation could have been maintained along the Y-shaped montane ranges (Sierra Madre del Oriental, Sierra Madre del Occidental, Sierra Madre del Sur and the Trans-Mexico Volcanic Belt) and have provided some refuge areas. The present distribution ranges of sexual diploids of some species of Stevia in Mexico indicate that diploids were not restricted to a single refuge during the last ice age.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant species biology 4 (1989), S. 0 
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Examinations of chromosome number voucher specimens show that sexual diploid and agamospermous polyploid plants of Eupatorium in Asia can be distinguished by morphology, fertility, and stainability of pollen grains. Using these criteria, reproductive systems (sexual vs. agamospermous) were estimated for 558 herbarium specimens of Eupatorium in East Asia. Of 22 taxa examined, six included both sexual and agamospermous specimens; those of one taxon were all agamospermous; and those of 15 taxa were all sexual. This result shows that 21 taxa are not agamospermous microspecies but are differentiated at the diploid level. Sexual populations of most taxa had restricted geographical distributions. Eupatorium chinense var. chinense and var. oppositifolium consisted of both sexual and agamospermous populations. Sexual populations of these two varieties were allopatric and distinct in external morphology, suggesting differentiation at the species level. The specimens of E. heterophyllum s. str. were all agamospermous, while those of E. mairel, often treated as synonymous with E. heterophyllum, were sexual.In comparing East Asian and North American Eupatorium for the distributional patterns of sexual and agamospermous populations, three differences can be pointed out: (1) Agamospermous plants of autopolyploid origin have evolved in eight species and are widespread in North America; while most agamospermous plants in East Asia may be of allopolyploid origin, have relatively restricted ranges, and are less frequent than the diploid plants with the exception of in E. chinense var. oppositifolium, (2) The number of sexual species with wide range is greater in North America than in East Asia. (3) The number of sexual species with restricted ranges is greater in East Asia than in North America. The results obtained suggest that speciation among the plants of Eupatorium has occurred more recently in East Asia than in North America.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Melbourne, Australia : Blackwell Science Pty
    Plant species biology 16 (2001), S. 0 
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Chromosome numbers from 244 accessions representing 73 species, five varieties and two putative species hybrids in Mexican Stevia are reported with comments on agamospermy, cytogeography and chromosomal evolution. The chromosome numbers of 47 species and two varieties were counted for the first time. Counts of 12 species and two varieties were new cytotypes, or differed from all previously reported numbers for the same species. B chromosomes were found in 16 species and two varieties. All species of shrubs or shrublets were sexual diploids (2n = 24). Perennial herbs were diploids or polyploids based on x = 11 or 12 and the widespread prevalence of agamospermous polyploids was revealed. Chromosome numbers of annual herbs varied from 2n = 24 to 2n = 8. The cytogeographical survey revealed five distributional patterns of agamic complexes based on the relative abundance of polyploids compared to their diploid ancestors. The wider distributional range (extending to northern and inland areas) of some agamospermous polyploids have been achieved by recent colonization accompanying climatic warming after the last glaciation. This has occurred even in lower latitudes such as Mexico, due to more successful founder population reproduction and the acceleration of seed dispersal, as well as the creation of new and open habitats by human activities.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Ainsliaea apiculata is a cleistogamous perennial. This species occasionally hybridizes with A. faurieana on Yakushima Island, Japan and the hybrids are fertile. A cytological study of these hybrids revealed no irregularity in their male meiosis and the occurrence of genetic segregation through successful reproduction. Allozyme variation provided evidence for segregation through selfing in the hybrids. Observation on pollen grain number showed that these hybrids have cleistogamous flowers in various frequencies. Cleistogamy is dominantly inherited in the hybrids and selfing by cleistogamous flowers is considered to contribute to the formation of hybrid populations.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant species biology 5 (1990), S. 0 
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Recent progress in research on the evolution of agamospermy in Boehmeria (Urticaceae) and Eupatorium (Asteraceae) is reviewed. Specific questions addressed are: (1) Is there any trend in distributions and habitat preferences of sexual and agamospermous races? (2) Is hybridity or a high level of heterozygosity a prerequisite for the evolution of agamospermous races? (3) Do agamospermous plants produce genetically variable offsprings through hybridization with sexual relatives? and (4) Do agamospermous plants have the theoretically predicted reproductive advantage over sexuals? From the results presented, the following conclusions can be drawn. (1) Sexual and agamospermous relatives are usually ecologically differentiated; sexuals tend to require extreme habitats, while agamosperms prefer disturbed places. (2) Hybridity or a high level of heterozygosity is not a prerequisite to the evolution of agamospermous races. (3) Agamospermous races produce genetically variable offspring through hybridization with sexual relatives and subsequent segregation. (4) Agamospermous plants have a reproductive advantage often greater than twofold; part of this advantage is attributed to polyploidy. The question of why agamospermous races do not replace sexuals remains open. Male recovery in agamosperms through hybridization and/or the disadvantage of polyploidy associated with agamospermy might work as mechanism(s) enabling sexuals to resist colonization of reproductively superior agamosperms under some extreme ecological conditions.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The frequency of hybrids was monitored using progenies grown from seeds collected from open-pollinated plants in mixed populations of Farfugium hiberniflorium and F. japonicum. The results showed that hybrids are more frequently derived from F. japonicum than from F. hiberniflorum. This directionality of hybridization and extraordinarily high frequency of hybrids among progenies grown from seeds from open-pollinated plants of F. japonicum enabled us to derive an empirical equation describing the frequency of hybridization as a decreasing exponential function of interspecific plant distance. The relationship between these two variables fitted a function describing pollen flow from a particular plant. This finding suggests that interspecific pollen exchange can be viewed simply as a process dependent of interspecific plant distance, and the actual rate of hybridization is determined by the level of cross-compatibility of a particular species.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant species biology 2 (1987), S. 0 
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Observations in two populations of Asarum caulescens belonging to sect. Asarum indicate that inbreeding predominates becuase (1) no effective pollinator was observed, (2) bagged flowers set fruits with well-swollen seeds, and (3) the behaviour of filaments, changing from recurved to straight posture, results in direct deposition of pollen grains on the stigmas. This result agrees with reports on three other species of sect. Asarum in Europe and North America. We suggest that species of sect. Asarum diverged from an autogamous ancestor.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 422 (2003), S. 831-831 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Man'yoshu, meaning 'collection of ten thousand leaves', is the largest and earliest anthology of Japanese poetry — it contains over 4,500 poems written between the early seventh century and the middle of the eighth century, and provides a glimpse of Japanese life during that period. ...
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-1939
    Keywords: Agamospermy ; Demography ; Eupatorium chinense ; Geminivirus ; Mortality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract There are few studies of the interaction between wild plants and viruses. In this paper, the incidence of a geminivirus (tobacco leaf curl virus, TLCV) infection, and its effects on mortality, growth and reproduction of its host-plant, Eupatorium chinense, are reported. A total of 221 plants of an agamospermous population of E. chinense were chosen and their demographic behaviour followed over 2 years (1991–1992). The proportion of infected plants differed between years, with fewer plants infected in 1991 than in 1992. Under low virus incidence (35.3% in 1991), infection was significantly associated with taller plants (〉80 cm). However, when the incidence of infected plants increased by almost two times (69.1%) in 1992, this tendency disappeared and small plants were also infected. Virus infection had significant effects on mortality of agamospermous plants. Almost half of the initial number of marked plants (n=221) died after 1 year of observations. Of those dead plants (n=105), 86 plants (82%) were infected in 1991, indicating that virus infection was an important, but not the sole cause of mortality. In 1992, 116 plants were alive, and of these, 40% were infected in 1991, indicating that some infected plants survived 1 year. Agamospermous plants were classified in three groups according to the extent of virus infection (plants infected in 2 years, infected in 1 year and uninfected plants) to detect the effect of virus infection on growth of plants of E. chinense. Infected plants had significantly lower growth rates than healthy plants. Infected plants also produced significantly fewer seeds than uninfected plants. Virus infection, however, had no significant effect on the probability of reproduction in plants of E. chinense, suggesting that infected plants may reproduce but with a lower seed output. In this study, we showed that virus infection may have a strong effect on demographic traits and, as a consequence, on fitness components of plants of E. chinense. These effects were higher than those sometimes observed in other plant-herbivore or plant-pathogen interactions.
    Type of Medium: Electronic Resource
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