Table of Contents
  • Volume 49 Issue 6

    Cover illustration: Clonal and sexual reproduction of Wolffia plants, the smallest angiosperm. A, Plants of Wolffia globosa (Roxb.) Hartog in clonal reproduction. B, Close-up view of W. globosa vegetative fronds showing mother frond (MF) and daughter fronds (DF). C, Close-up view of W. globosa fronds showing maturation of minute protogynous flowers. D, Several flowering fronds under natural condition. Photographed by Jun-Xia YUAN and Qing HUANG. See YUAN et al., pp. 509–517 in this issue.
      
      Research Articles
    • Jun-Xia YUAN, Jin PAN, Bao-Sheng WANG, Da-Ming ZHANG
      2011, 49 (6): 509–517
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      Wolffia Horkel ex Schleid. (Lemnaceae) includes the world's smallest angiosperms. Morphologically, their bodies are extremely simplified, making classification difficult and long-disputed. No reports about the genetic structure of these clonal-dominant aquatic plants have been published until now. In this study, of 247 samples from 42 populations spanning representative locations in China, two chloroplast haplotypes (glo-cp and un-cp) and 66 amplified fragment length polymorphism genotypes were identified. Based on wide sampling, cpDNA haplotypes, and amplified fragment length polymorphism profiles, we found that there are two genetic lineages (glo- and un- lineages) of Wolffia species in China. Genotypic and genetic diversity of Wolffia species are high compared with other clonal plants (Simpson's index, D= 0.97; Nei's diversity, H= 0.1835). Different spatial structure patterns were detected between glo- and un- lineages. Positive autocorrelation at short distances (<400 km) and slightly negative autocorrelations at larger distances (>1500 km) were detected within the glo-lineage, but no significant spatial genetic structure was detected beyond 100 km within the un-lineage. Overall, spatial genetic analysis of W. globosa revealed significant autocorrelation within short distances, indicating that restricted gene flow might be one of the most important factors in shaping genetic structure.
    • Shou-Zhou ZHANG, Ya-Ling WANG, Zi-Can HE, Erland EJDER
      2011, 49 (6): 518–527
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      The cross compatibility within and between Yulania Spach and Michelia L. (Magnoliaceae) is relatively good and various such hybrids, obtained by conventional artificial hybridization, are available. The aim of the present study was to determine the extent of genome differentiation between the species involved in these crosses through the observation of chromosome pairing during meiosis in pollen mother cells (PMCs) of the hybrids. Chromosome pairing behavior was studied in five species (2n = 38) and two interspecific hybrids of Michelia, eight species (2n = 38, 76 and 114) and 10 interspecific hybrids of Yulania, and three intergeneric hybrids between Michelia and Yulania. The results showed that chromosome pairing was normal with bivalent formation in diploid parental species and in interspecific hybrids. In addition to bivalents, multivalents were encountered in polyploid parental species and polyploid interspecific hybrids. In the intergeneric hybrids between a tetraploid Yulania and two diploid Michelia, 19 chromosomes, most likely originating from Michelia, were unable to synapse from zygotene to metaphase I. Meiotic chromosome pairing indicated a high degree of homology between species within Michelia and Yulania and less homology between the genomes of these two genera. The differentiation of morphological characters and the distinctness of natural distribution also support the conclusion that these two genera are likely independent monophyletic groups. This suggests that the two genera were split at early evolution of Magnoliaceae and the overlapping characteristics in external morphology and internal structures of the two genera may be the result of parallel evolution or ancient common ancestry.
    • Yang LIU, Chun-Ce GUO, Gui-Xia XU, Hong-Yan SHAN, Hong-Zhi KONG
      2011, 49 (6): 528–538
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      Previous studies on Arabidopsis thaliana and other model plants have indicated that the development of a flower is controlled by a regulatory network composed of genes and the interactions among them. Studies on the evolution of this network will therefore help understand the genetic basis that underlies flower evolution. In this study, by reviewing the most recent published work, we added 31 genes into the previously proposed regulatory network for flower development. Thus, the number of genes reached 60. We then compared the composition, structure, and evolutionary rate of these genes between A. thaliana and one of its allies, A. lyrata. We found that two genes (FLC and MAF2) show 1: 2 and 2: 2 relationships between the two species, suggesting that they have experienced independent, post-speciation duplications. Of the remaining 58 genes, 35 (60.3%) have diverged in exon–intron structure and, consequently, code for proteins with different sequence features and functions. Molecular evolutionary analyses further revealed that, although most floral genes have evolved under strong purifying selection, some have evolved under relaxed or changed constraints, as evidenced by the elevation of nonsynonymous substitution rates and/or the presence of positively selected sites. Taken together, these results suggest that the regulatory network for flower development has evolved rather rapidly, with changes in the composition, structure, and functional constraint of genes, as well as the interactions among them, being the most important contributors.
    • Hong YAO, Yi-Bo LUO
      2011, 49 (6): 539–545
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      Pollination limitation is common in flowering plants and is thought to be a factor driving the evolution of floral traits. The plasticity of floral longevity to pollination may be an adaptation of plants to pollen limitation. However, this adaptation is less critical in short-lived flowers. To evaluate pollen limitation and the plasticity of floral longevity to pollination in Potentilla tanacetifolia, a gynodioecious herb with short-lived flowers, we analyzed its breeding system, tested sex-differential pollen limitation, and compared variations in floral display size in natural populations in Duolun County, Inner Mongolia, China. Hand pollination experiments and pollinator exclusion treatments revealed that P. tanacetifolia is self-compatible and non-autonomously apomictic and shows sex-differential pollen limitation. The plasticity of floral longevity to pollination was observed; the floral duration of female plants was prolonged by approximately 3–4 hours with pollination exclusion treatment. Moreover, the percentage of flowers displayed on female plants during pollination exclusion treatment was significantly higher than that during natural pollination. Under natural pollination conditions, the percentage of flowers displayed on female plants was significantly higher than on hermaphrodite plants. Furthermore, approximately 50% of the pollen grains spread out of the anthers of hermaphrodite flowers within 2 h of anthesis; the number of pollen grains adhering to the stigmas of hermaphrodite flowers was significantly higher than that adhering to female flowers when flowers shed their petals. These results indicate that variation in floral longevity may be an adaptive strategy to pollination conditions for gynodioecious P. tanacetifolia.
    • Lei XU, Rhett D. HARRISON, Pei YANG, Da-Rong YANG
      2011, 49 (6): 546–557
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      Studies on the evolution of tropical taxa emphasize the role of vicariance and the break-up of Gondwana in explaining modern distributions. Earlier studies on figs (Ficus spp.) support this view. In the current study, we used an expanded sample (208 spp.) and improved molecular dating techniques to reconstruct the phylogenetic and biogeographic history of Ficus. Consistent with previous studies, our biogeographic analysis indicated that the ancestor of Ficus was present in Gondwana. However, a relaxed clock analysis relying on uncorrelated rates in BEAST suggested that the Neotropical section Pharmacosycea split-off in South America 86.67 Mya, and that other Ficus lineage ancestors originated in India. Most of the basal lineages appeared to have diverged following KT extinction, then rapidly diversified after India collided with continental Asia. The Afrotropical species most likely evolved initially in the Indian subcontinent then dispersed to Africa, either in the late Cretaceous of Madagascar or even later, following the Eocene collision of India with Asia. The Neotropical section Americana, either island-hopped to South America or took a northern route to the Americas through Europe prior to the terminal Eocene global cooling event. Ficus may have arrived in eastern Malesia following the collision of India with Asia, then widely dispersed thereafter. Given the wide ranges in our date estimates, several other scenarios are possible. However, contrary to earlier reports, our analyses suggest that vicariance played a relatively minor role compared with ecological opportunity and dispersal in the diversification of genus Ficus.
    • Chang-Bao WANG, Xiang-Guang MA, Xing-Jin HE
      2011, 49 (6): 558–589
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      As one of the big genera in Apiaceae, Bupleurum L. has received considerable attention from plant taxonomists. Nevertheless, there are still many gaps in our knowledge of this genus, especially of those species endemic to China that have often been excluded from previous studies. In spite of a few recent studies on the phylogeny and classification of the Chinese Bupleurum, the most essential problem of species delimitation still remains unresolved. We re-evaluate the taxonomy of the Chinese Bupleurum using morphological and molecular evidence. Careful observations of living plants growing the field and herbarium specimens were made to understand the morphological variation and to ensure species identification for the molecular analysis. Phylogenetic analyses were carried out on sequence data of nuclear ribosomal internal transcribed spacer (nrITS), trnH-psbA, and matK, using parsimony and Bayesian approaches to evaluate species relationships. Analyses of both nrITS and combined datasets of the three regions revealed the following results: (i) the Chinese Bupleurum species were divided into two major lineages; and (ii) most species were well defined, but some traditional inter- and infraspecific relationships were not supported. Our results, along with the results of previous works support that the Chinese Bupleurum species were derived from two different lineages and should be placed in Neves and Watson's subgenus Bupleurum. Our detailed taxonomic re-assessment of several Chinese species resulted in new taxonomic recombinations with rank changes for three species: Bupleurum tenerum, B. amplexicaule, and B. franchetii; new combination for one variety, B. smithii var. flaviflorum; and the description of one variety and one species, B. stenophyllum var. leiocarpum and B. sikangense.
    • Yun GUO, De-Ming WANG
      2011, 49 (6): 590–597
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      Archaeopteris macilenta is one of the most widespread plants in the Late Devonian. Based on fossils from the Frasnian Huangjiadeng Formation, Yichang District of Hubei Province, for the first time we study in detail the anatomy of this progymnosperm plant in South China. Ultimate axes are protostelic with three xylem sympodia and lack secondary tissue. Penultimate axes are eustelic, bearing eight sympodia and a thin band of secondary xylem. Radially symmetrical sympodia of mesarch primary xylem produce traces of appendages in a spiral arrangement. Archaeopteris macilenta and A. halliana (A. roemeriana) are dominant in the Frasnian and Famennian, respectively. Comparisons with these two species from other tectonic plates indicate consistent stelar architectures. Global spread, continuous occurrence, and identical anatomy during the Late Devonian indicate that Archaeopteris survived the Frasnian–Famennian extinction event. In this time, endemic genera and cosmopolitan taxa, including Archaeopteris, suggest the palaeogeographic isolation of South China and certain associations with other plates.
    • Guo-Wei ZHOU, Hui HUANG
      2011, 49 (6): 598–605
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      Endosymbiotic dinoflagellates in the genus Symbiodinium are among the most abundant and important group of photosynthetic protists found in coral reef ecosystems. In order to further characterize this diversity and compare with other regions of the Pacific, samples from 44 species of scleractinian corals representing 20 genera and 9 families, were collected from tropical reefs in southern Hainan Island, China. Denaturing gradient gel electrophoresis fingerprinting of the ribosomal internal transcribed spacer 2 identified 11 genetically distinct Symbiodinium types that have been reported previously. The majority of reef-building coral species (88.6%) harbored only one subcladal type of symbiont, dominated by host-generalist C1 and C3, and was influenced little by the host's apparent mode of symbiont acquisition. Some species harbored more than one clade of Symbiodinium (clades C, D) concurrently. Although geographically isolated from the rest of the Pacific, the symbiont diversity in southern Hainan Island was relatively low and similar to both the Great Barrier Reef and Hawaii symbiont assemblages (dominated by clade C Symbiodinium). These results indicate that a specialist symbiont is not a prerequisite for existence in remote and isolated areas, but additional work in other geographic regions is necessary to test this idea.
    • Haifeng GU
      2011, 49 (6): 606–616
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      Alexandrium ostenfeldii is a potentially toxic dinoflagellate that often occurs in coastal areas at high latitudes. Here we report the presence of A. ostenfeldii in the Bohai Sea, China, for the first time. The vegetative cells of A. ostenfeldii are characterized by a narrow first apical plate and a large ventral pore located on the anterior right side. Partial large subunit sequence comparison revealed that the Chinese strain differs from the Finnish strains at only three positions, and from A. peruvianum of Spain at five positions. Maximum parsimony analysis revealed that A. ostenfeldii from China and Finland and A. peruvianum from Spain grouped together. They were the nearest sister group to a clade with A. ostenfeldii from New Zealand, Europe, and North America. In culture, growth did not occur at temperatures below 9 °C and occurred at salinities between 7 and 27 psu. It took 10–20 days for newly formed cysts to mature at 20 °C. Lower temperature delayed germination, but the germination rate exceeded 90% at temperatures from 12 to 24 °C. No germination occurred below 9 °C after 1 month of incubation. The Chinese strain of A. ostenfeldii produced neither spirolides nor paralytic shellfish poisoning toxins.
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Editors-in-Chief
Song Ge
Jun Wen
Impact Factor
2.779
JCR 2019 IF ranking: 56/234 (Plant Sciences, top 23.72%, Q1 quartile)
Journal Abbreviation: J Syst Evol
ISSN: 1674-4918 (Print)
1759-6831 (Online)
CN: 11-5779/Q
Frequency: Bi-monthly

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