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资助项目
0.05) between wild (AR = 4.651), semi-cultivated (AR = 5.091) and cultivated (AR = 5.132) populations of C. taliensis, which suggested that the genetic background of long-lived woody plant was not easy to be changed, and there were moderate high gene flow between populations. However, there was a significant difference (P < 0.05) between wild (AR = 5.9) and cultivated (AR = 7.1) populations distributed in the same place in Yun county, Yunnan province, which may result from the hybridization and introgression of species in the tea garden and anthropogenic damages to the wild population. The hypothesis of hybrid origin of C. grandibracteata was tested by morphological and microsatellites analyses. Compared with other species, the locules in ovary of C. grandibracteata are variable, which showed a morphological intermediate and mosaic. Except one private allele, Ninety-nine percent alleles of C. grandibracteata were shared with these of C. taliensis and C. sinensis var. assamica. And C. grandibracteata was nested in the cluster of C. taliensis in the UPGMA tree. Conclusively, our results supported the hypothesis of hybrid origin of C. grandibracteata partly. The speciation of C. grandibracteata was derived from hybridization and asymmetrical introgression potentially. It is possible that C. taliensis was one of its parents, but it still needs more evidences to prove that C. sinensis var. assamica was another 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tree.%5C+Conclusively%2C%5C+our%5C+results%5C+supported%5C+the%5C+hypothesis%5C+of%5C+hybrid%5C+origin%5C+of%5C+C.%5C+grandibracteata%5C+partly.%5C+The%5C+speciation%5C+of%5C+C.%5C+grandibracteata%5C+was%5C+derived%5C+from%5C+hybridization%5C+and%5C+asymmetrical%5C+introgression%5C+potentially.%5C+It%5C+is%5C+possible%5C+that%5C+C.%5C+taliensis%5C+was%5C+one%5C+of%5C+its%5C+parents%2C%5C+but%5C+it%5C+still%5C+needs%5C+more%5C+evidences%5C+to%5C+prove%5C+that%5C+C.%5C+sinensis%5C+var.%5C+assamica%5C+was%5C+another%5C+parent."},{"jsname":"Chiang Mai University","jscount":"1","jsurl":"/simple-search?field1=all&field=dc.citation.source_filter&advanced=false&query1=POACEAE&&fq=dc.project.title_filter%3AChiang%5C+Mai%5C+University"},{"jsname":"China Postdoctoral Science Foundation","jscount":"1","jsurl":"/simple-search?field1=all&field=dc.citation.source_filter&advanced=false&query1=POACEAE&&fq=dc.project.title_filter%3AChina%5C+Postdoctoral%5C+Science%5C+Foundation"},{"jsname":"Chinese Academy of Sciences","jscount":"1","jsurl":"/simple-search?field1=all&field=dc.citation.source_filter&advanced=false&query1=POACEAE&&fq=dc.project.title_filter%3AChinese%5C+Academy%5C+of%5C+Sciences"},{"jsname":"Chinese Academy of Sciences[2013T2S0030]","jscount":"1","jsurl":"/simple-search?field1=all&field=dc.citation.source_filter&advanced=false&query1=POACEAE&&fq=dc.project.title_filter%3AChinese%5C+Academy%5C+of%5C+Sciences%5C%5B2013T2S0030%5C%5D"},{"jsname":"Craigia yunnanensis W. W. Smith & W. E. Evans (Tiliaceae) is an endangered deciduous tree species which has high scientific and economic value. C. yunnanensis is seriously threatened and has been pushed to the verge of extinction due to vegetation destruction in China and consequent contraction of its distribution. Hence, it was listed as a nationally rare and endangered plant in 1999 and has also been proposed as a second-ranked plant for national protection in China and included in IUCN red list. As a scientifically important and valued tree species with endangered status, the wild populations of C. yunnanensis therefore represent is a genetic resource that must be conserved. To provide basic information for its conservation, the population dynamics and population size structures, pollination biology and breeding system, eleven fitness-related characters and the genetic variability based on AFLP were comprehensively studied. The main results are summarized as follows: A total of six wild populations of C. yunnanensis were found in two disjunct regions of Yunnan, i.e. WenShan (SE Yunnan) and DeHong (SW Yunnan), from 2005 to 2007. Additionally, in all but one of the populations we detected, mature trees were felled between 2005 and 2007, so destruction of most of these populations is ongoing. Across the six populations of extant C. yunnanensis found during our study, the total number of mature (reproductive) individuals detected was 584 in 2007，plus larger numbers of seedling and resprouts from cut trunks. The result of surveying Population structure showed that there are two regeneration types which are seedlings and sprouts. Seedlings occurred abundantly in gaps or open areas and the size class frequency distributions were often discontinuous, and the same general pattern occurred in all the investigated populations for juveniles and adults. The numbers of seed-origin individuals did however decline sharply with increasing size, indicating a high mortality rate going from seedling to sapling stage may be a problem for this species. Additionally, the cash crop cultivation and logging seriously threaten the survival of the species. We conducted field observations and artificial pollination experiments on the floral biology, pollination process and breeding system of Craigia yunnanensis in Fadou, Xichou county of Yunnan province. The lifespan of a single hermaphrodite flower is approximately 3-4 days. A cyme has 2-9 flowered. The flowering period of an inflorescence is usually 5-14 days. The flowers of C. yunnanensis were protandrous. The stamens were within petal-like staminodes in the opening flowers until the flower withered. Without touchment, the bractlike staminodes can’t open. Self-pollination was partially avoided by temporal and spatial isolation of male and female organs within the same flower. However, autogamous and geitonogamous pollination is unavoidable because of the large number of flowers on a single tree and the action of pollinators. The values of both OCI (≥4) and P/O (1381) and the results of bagging tests indicated there was no apomixes in C. yunnanensis and the breeding system of the species was outcrossing with partial self-compatibility and the pollinators were required during the pollination process. The most frequent effective floral visitor was only beautiful fly (Chrysomyia megacephala). Fruit set and seed set in natural condition were 56.67±3.85％ and 6.26±0.75％, respectively. Therefore, lack of pollinators, low pollination efficiency, unavoidable geitonogamous pollination and partial self-compatibility and inbreeding in small populations may account for the low fruit set, especially seed set.Variations in seed traits, seed germination, and seedling growth characters among six Craigia yunnanensis populations were evaluated. All seed and seedling traits exhibited significant differences among populations (P < 0.05). The fitness of seed as assessed by seed size, seed germination and seedling trait was independent of population size, except for the number of seeds per capsule (r = 0.93，P < 0.01). Correlations between geo-climatic variables of seed origin and seed and seedling related characters were insignificant (P > 0.05). For some populations, germination capacity in 12-h photoperiod was significantly higher than that in completed darkness（W-FD: P < 0.01, W-JD: P < 0.05）.Genetic variation within and among six populations was assessed using AFLP markers. Genetic diversity was higher at species level (PPL = 69.19%, HE = 0.221) than at population level (PPL = 26.22%, HE = 0.095, Is =0.140), and populations in southeast Yunnan were strongly differentiated from those in southwest Yunnan (Nei’s GST = 0.575; FST = 0.655). UPGMA analysis demonstrated a clear genetic division between the two populations from DeHong (SW Yunnan; D-JD and D-HG) and the four from WenShan (SE Yunnan; W-FD, W-LH, W-ML, and W-MG). Within-population genetic variation was significantly correlated with population isolation (r(PPL) = -0.94, P = 0.006; r(HE) = -0.85, P = 0.032; r(Is) = -0.87, P = 0.025), but not with population size (r(PPL) = 0.63, P = 0.178; r(HE) = 0.54, P = 0.268; r(Is) = 0.56, P = 0.249).","jscount":"1","jsurl":"/simple-search?field1=all&field=dc.citation.source_filter&advanced=false&query1=POACEAE&&fq=dc.project.title_filter%3ACraigia%5C+yunnanensis%5C+W.%5C+W.%5C+Smith%5C+%5C%26%5C+W.%5C+E.%5C+Evans%5C+%5C%28Tiliaceae%5C%29%5C+is%5C+an%5C+endangered%5C+deciduous%5C+tree%5C+species%5C+which%5C+has%5C+high%5C+scientific%5C+and%5C+economic%5C+value.%5C+C.%5C+yunnanensis%5C+is%5C+seriously%5C+threatened%5C+and%5C+has%5C+been%5C+pushed%5C+to%5C+the%5C+verge%5C+of%5C+extinction%5C+due%5C+to%5C+vegetation%5C+destruction%5C+in%5C+China%5C+and%5C+consequent%5C+contraction%5C+of%5C+its%5C+distribution.%5C+Hence%2C%5C+it%5C+was%5C+listed%5C+as%5C+a%5C+nationally%5C+rare%5C+and%5C+endangered%5C+plant%5C+in%5C+1999%5C+and%5C+has%5C+also%5C+been%5C+proposed%5C+as%5C+a%5C+second%5C-ranked%5C+plant%5C+for%5C+national%5C+protection%5C+in%5C+China%5C+and%5C+included%5C+in%5C+IUCN%5C+red%5C+list.%5C+As%5C+a%5C+scientifically%5C+important%5C+and%5C+valued%5C+tree%5C+species%5C+with%5C+endangered%5C+status%2C%5C+the%5C+wild%5C+populations%5C+of%5C+C.%5C+yunnanensis%5C+therefore%5C+represent%5C+is%5C+a%5C+genetic%5C+resource%5C+that%5C+must%5C+be%5C+conserved.%5C+To%5C+provide%5C+basic%5C+information%5C+for%5C+its%5C+conservation%2C%5C+the%5C+population%5C+dynamics%5C+and%5C+population%5C+size%5C+structures%2C%5C+pollination%5C+biology%5C+and%5C+breeding%5C+system%2C%5C+eleven%5C+fitness%5C-related%5C+characters%5C+and%5C+the%5C+genetic%5C+variability%5C+based%5C+on%5C+AFLP%5C+were%5C+comprehensively%5C+studied.%5C+The%5C+main%5C+results%5C+are%5C+summarized%5C+as%5C+follows%5C%3A%5C+A%5C+total%5C+of%5C+six%5C+wild%5C+populations%5C+of%5C+C.%5C+yunnanensis%5C+were%5C+found%5C+in%5C+two%5C+disjunct%5C+regions%5C+of%5C+Yunnan%2C%5C+i.e.%5C+WenShan%5C+%5C%28SE%5C+Yunnan%5C%29%5C+and%5C+DeHong%5C+%5C%28SW%5C+Yunnan%5C%29%2C%5C+from%5C+2005%5C+to%5C+2007.%5C+Additionally%2C%5C+in%5C+all%5C+but%5C+one%5C+of%5C+the%5C+populations%5C+we%5C+detected%2C%5C+mature%5C+trees%5C+were%5C+felled%5C+between%5C+2005%5C+and%5C+2007%2C%5C+so%5C+destruction%5C+of%5C+most%5C+of%5C+these%5C+populations%5C+is%5C+ongoing.%5C+Across%5C+the%5C+six%5C+populations%5C+of%5C+extant%5C+C.%5C+yunnanensis%5C+found%5C+during%5C+our%5C+study%2C%5C+the%5C+total%5C+number%5C+of%5C+mature%5C+%5C%28reproductive%5C%29%5C+individuals%5C+detected%5C+was%5C+584%5C+in%5C+2007%EF%BC%8Cplus%5C+larger%5C+numbers%5C+of%5C+seedling%5C+and%5C+resprouts%5C+from%5C+cut%5C+trunks.%5C+The%5C+result%5C+of%5C+surveying%5C+Population%5C+structure%5C+showed%5C+that%5C+there%5C+are%5C+two%5C+regeneration%5C+types%5C+which%5C+are%5C+seedlings%5C+and%5C+sprouts.%5C+Seedlings%5C+occurred%5C+abundantly%5C+in%5C+gaps%5C+or%5C+open%5C+areas%5C+and%5C+the%5C+size%5C+class%5C+frequency%5C+distributions%5C+were%5C+often%5C+discontinuous%2C%5C+and%5C+the%5C+same%5C+general%5C+pattern%5C+occurred%5C+in%5C+all%5C+the%5C+investigated%5C+populations%5C+for%5C+juveniles%5C+and%5C+adults.%5C+The%5C+numbers%5C+of%5C+seed%5C-origin%5C+individuals%5C+did%5C+however%5C+decline%5C+sharply%5C+with%5C+increasing%5C+size%2C%5C+indicating%5C+a%5C+high%5C+mortality%5C+rate%5C+going%5C+from%5C+seedling%5C+to%5C+sapling%5C+stage%5C+may%5C+be%5C+a%5C+problem%5C+for%5C+this%5C+species.%5C+Additionally%2C%5C+the%5C+cash%5C+crop%5C+cultivation%5C+and%5C+logging%5C+seriously%5C+threaten%5C+the%5C+survival%5C+of%5C+the%5C+species.%5C+We%5C+conducted%5C+field%5C+observations%5C+and%5C+artificial%5C+pollination%5C+experiments%5C+on%5C+the%5C+floral%5C+biology%2C%5C+pollination%5C+process%5C+and%5C+breeding%5C+system%5C+of%5C+Craigia%5C+yunnanensis%5C+in%5C+Fadou%2C%5C+Xichou%5C+county%5C+of%5C+Yunnan%5C+province.%5C+The%5C+lifespan%5C+of%5C+a%5C+single%5C+hermaphrodite%5C+flower%5C+is%5C+approximately%5C+3%5C-4%5C+days.%5C+A%5C+cyme%5C+has%5C+2%5C-9%5C+flowered.%5C+The%5C+flowering%5C+period%5C+of%5C+an%5C+inflorescence%5C+is%5C+usually%5C+5%5C-14%5C+days.%5C+The%5C+flowers%5C+of%5C+C.%5C+yunnanensis%5C+were%5C+protandrous.%5C+The%5C+stamens%5C+were%5C+within%5C+petal%5C-like%5C+staminodes%5C+in%5C+the%5C+opening%5C+flowers%5C+until%5C+the%5C+flower%5C+withered.%5C+Without%5C+touchment%2C%5C+the%5C+bractlike%5C+staminodes%5C+can%E2%80%99t%5C+open.%5C+Self%5C-pollination%5C+was%5C+partially%5C+avoided%5C+by%5C+temporal%5C+and%5C+spatial%5C+isolation%5C+of%5C+male%5C+and%5C+female%5C+organs%5C+within%5C+the%5C+same%5C+flower.%5C+However%2C%5C+autogamous%5C+and%5C+geitonogamous%5C+pollination%5C+is%5C+unavoidable%5C+because%5C+of%5C+the%5C+large%5C+number%5C+of%5C+flowers%5C+on%5C+a%5C+single%5C+tree%5C+and%5C+the%5C+action%5C+of%5C+pollinators.%5C+The%5C+values%5C+of%5C+both%5C+OCI%5C+%5C%28%E2%89%A54%5C%29%5C+and%5C+P%5C%2FO%5C+%5C%281381%5C%29%5C+and%5C+the%5C+results%5C+of%5C+bagging%5C+tests%5C+indicated%5C+there%5C+was%5C+no%5C+apomixes%5C+in%5C+C.%5C+yunnanensis%5C+and%5C+the%5C+breeding%5C+system%5C+of%5C+the%5C+species%5C+was%5C+outcrossing%5C+with%5C+partial%5C+self%5C-compatibility%5C+and%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species, usually called tree ferns, are considered as relicts of a time when dinosaurs were common. In recent several decades, the number of Cyatheaceae plants decreases dramatically. In order to find the reasons and provide directions for protecting these endangered plants, the biological characteristics of Cyatheaceae were surveyed. Using AFLP and cpDNA sequence variations, the genetic diversity and phylogeography of Sphaeropteris brunoniana were also analyzed. Based on these findings, implications for conservation strategies were discussed for this relict tree fern. Main results of the dissertation were summarized as follows, (1) Cyatheaceae plants have extensive distribution in Yunnan, China, and most of them distribute in southeast of Yunnan. In southeast, they usually inhabit margins of evergreen broad-leaved forests or secondary coniferous forests; however, the population update is very different and the age structure is unscientific. The spore of Cyatheaceae is trilete, radially symmetrical, and perinous. The spores of Alsophila species feature a ridged perine and a granular, verrucate or smooth exine. The spores of S. brunoniana are characterized by an incipient granular outermost layer and a verrucate exine. The metaphase chromosome numbers of gametophytes in the three examined species, viz. A. podophylla, A. gigantea and A. austro-yunnanensis, are 69, indicating that they are diploid and do not display variety in chromosome number. The chemical constituents of S. brunoniana are main simple and familiar compounds, such as saccharides, fatty acids and alcohols, and stigmasterols. (2) An unexpectedly high level of nDNA genetic diversity and low cpDNA diversity were detected in S. brunoniana. (3) This study showed that the genetic differentiation among populations within regions was low and between regions was significant. (4) There were several refugia of S. brunoniana in Yunnan during glacial periods. The Hainan populations were likely new colonizations and originated from Southeast Asia. (5) To retain existing genetic diversity, whether in situ or ex situ conservation or collection of germplasm is used, the populations of the two regions should be considered equally. Furthermore, ex situ conservation of this species should be preferably conducted on large populations.","jscount":"1","jsurl":"/simple-search?field1=all&field=dc.citation.source_filter&advanced=false&query1=POACEAE&&fq=dc.project.title_filter%3ACyatheaceae%5C+species%2C%5C+usually%5C+called%5C+tree%5C+ferns%2C%5C+are%5C+considered%5C+as%5C+relicts%5C+of%5C+a%5C+time%5C+when%5C+dinosaurs%5C+were%5C+common.%5C+In%5C+recent%5C+several%5C+decades%2C%5C+the%5C+number%5C+of%5C+Cyatheaceae%5C+plants%5C+decreases%5C+dramatically.%5C+In%5C+order%5C+to%5C+find%5C+the%5C+reasons%5C+and%5C+provide%5C+directions%5C+for%5C+protecting%5C+these%5C+endangered%5C+plants%2C%5C+the%5C+biological%5C+characteristics%5C+of%5C+Cyatheaceae%5C+were%5C+surveyed.%5C+Using%5C+AFLP%5C+and%5C+cpDNA%5C+sequence%5C+variations%2C%5C+the%5C+genetic%5C+diversity%5C+and%5C+phylogeography%5C+of%5C+Sphaeropteris%5C+brunoniana%5C+were%5C+also%5C+analyzed.%5C+Based%5C+on%5C+these%5C+findings%2C%5C+implications%5C+for%5C+conservation%5C+strategies%5C+were%5C+discussed%5C+for%5C+this%5C+relict%5C+tree%5C+fern.%5C+Main%5C+results%5C+of%5C+the%5C+dissertation%5C+were%5C+summarized%5C+as%5C+follows%2C%5C+%5C%281%5C%29%5C+Cyatheaceae%5C+plants%5C+have%5C+extensive%5C+distribution%5C+in%5C+Yunnan%2C%5C+China%2C%5C+and%5C+most%5C+of%5C+them%5C+distribute%5C+in%5C+southeast%5C+of%5C+Yunnan.%5C+In%5C+southeast%2C%5C+they%5C+usually%5C+inhabit%5C+margins%5C+of%5C+evergreen%5C+broad%5C-leaved%5C+forests%5C+or%5C+secondary%5C+coniferous%5C+forests%5C%3B%5C+however%2C%5C+the%5C+population%5C+update%5C+is%5C+very%5C+different%5C+and%5C+the%5C+age%5C+structure%5C+is%5C+unscientific.%5C+The%5C+spore%5C+of%5C+Cyatheaceae%5C+is%5C+trilete%2C%5C+radially%5C+symmetrical%2C%5C+and%5C+perinous.%5C+The%5C+spores%5C+of%5C+Alsophila%5C+species%5C+feature%5C+a%5C+ridged%5C+perine%5C+and%5C+a%5C+granular%2C%5C+verrucate%5C+or%5C+smooth%5C+exine.%5C+The%5C+spores%5C+of%5C+S.%5C+brunoniana%5C+are%5C+characterized%5C+by%5C+an%5C+incipient%5C+granular%5C+outermost%5C+layer%5C+and%5C+a%5C+verrucate%5C+exine.%5C+The%5C+metaphase%5C+chromosome%5C+numbers%5C+of%5C+gametophytes%5C+in%5C+the%5C+three%5C+examined%5C+species%2C%5C+viz.%5C+A.%5C+podophylla%2C%5C+A.%5C+gigantea%5C+and%5C+A.%5C+austro%5C-yunnanensis%2C%5C+are%5C+69%2C%5C+indicating%5C+that%5C+they%5C+are%5C+diploid%5C+and%5C+do%5C+not%5C+display%5C+variety%5C+in%5C+chromosome%5C+number.%5C+The%5C+chemical%5C+constituents%5C+of%5C+S.%5C+brunoniana%5C+are%5C+main%5C+simple%5C+and%5C+familiar%5C+compounds%2C%5C+such%5C+as%5C+saccharides%2C%5C+fatty%5C+acids%5C+and%5C+alcohols%2C%5C+and%5C+stigmasterols.%5C+%5C%282%5C%29%5C+An%5C+unexpectedly%5C+high%5C+level%5C+of%5C+nDNA%5C+genetic%5C+diversity%5C+and%5C+low%5C+cpDNA%5C+diversity%5C+were%5C+detected%5C+in%5C+S.%5C+brunoniana.%5C+%5C%283%5C%29%5C+This%5C+study%5C+showed%5C+that%5C+the%5C+genetic%5C+differentiation%5C+among%5C+populations%5C+within%5C+regions%5C+was%5C+low%5C+and%5C+between%5C+regions%5C+was%5C+significant.%5C+%5C%284%5C%29%5C+There%5C+were%5C+several%5C+refugia%5C+of%5C+S.%5C+brunoniana%5C+in%5C+Yunnan%5C+during%5C+glacial%5C+periods.%5C+The%5C+Hainan%5C+populations%5C+were%5C+likely%5C+new%5C+colonizations%5C+and%5C+originated%5C+from%5C+Southeast%5C+Asia.%5C+%5C%285%5C%29%5C+To%5C+retain%5C+existing%5C+genetic%5C+diversity%2C%5C+whether%5C+in%5C+situ%5C+or%5C+ex%5C+situ%5C+conservation%5C+or%5C+collection%5C+of%5C+germplasm%5C+is%5C+used%2C%5C+the%5C+populations%5C+of%5C+the%5C+two%5C+regions%5C+should%5C+be%5C+considered%5C+equally.%5C+Furthermore%2C%5C+ex%5C+situ%5C+conservation%5C+of%5C+this%5C+species%5C+should%5C+be%5C+preferably%5C+conducted%5C+on%5C+large%5C+populations."},{"jsname":"Cycas micholitzii complex is composed of 5 species: C. micholitzii Dyer, C. bifida (Dyer) K. D. Hill,C. longipetiolula D. Y. Wang, C. debaoensis Y. C. Zhong et C J. Chen, C. multipinnata C J. Chen et S. Y. Yang，and distributed from southwest China to central Vietnam and eastern Laos. Based on sequence data from two maternally inherited cpDNA and one biparentally nuclear DNA fragments, our study revealed the population genetic structure of C. micholitzii complex and explored the potential causes. The evolutionary and demographic histories were investigated. The genetic relationship among species in the complex was also clarified.The results were summarized as follows: 1. Phylogeographic analysis based on chloroplast sequences，We examined chloroplast sequence variation of the atpB-rbcLand psbA-trnHintergenic spacers in 27 populations of C. micholitzii complex, recovering 26 haplotypes. The average within-population diversity (HS = 0.140) was low while total diversity (HT = 0.911) was high. Population differentiation was also high(GST = 0.846, NST = 0.919), indicating significant phylogeographical structure (NST > GST,p < 0.001) and low levels of seed-based gene flow. C. debaoensis (Cycadaceae) is an endangered species restricted to the border of Guangxi and Yunnan province in southwest China. This species has been classified into two types: sand and karst, according to the soil matrix they grow on. We examined chloroplast sequence variation of the cpDNA sequences from 11 populations of this species. Significant population genetic differentiation was detected (GST= 0.684 and FST = 0.74160). There was marked genetic differentiation between populations in the sand and karst regions and no expansion was detected. Climate changes during glacial periods have had significant effects on the current distribution of cycads. The molecular phylogenetic data, together with the geographic distribution of the haplotypes, suggest that C. debaoensis experienced range contraction during glacial periods, and that the current populations are still confined to the original refugia in southwest China which have favorable habitats in glacial period. These results imply that small refugia were maintained in both sand and karst regions during the LGM (last glacial maximum). This species had no postglacial recolonization and only stayed in these refugia up to now. The low within-population diversity of C. debaoensis suggests that there were strong bottleneck events or founder effects within each separate region during the Quaternary climatic oscillations. Relatively high genetic and haplotype diversities were detected in the newly discovered populations, which located at intermediate locality of sand regions and had morphological variation; this is probably the consequence of the admixture of different haplotypes colonizing the area from separate sources. C. micholitzii occurs in the Annan Highlands in central Vietnam near the Laos border. C. bifida occurs in North Vietnam; its distribution extends across the border into adjacent localities in Guangxi and Yunnan in China. For the comparability between them,theywere considered as the same species C. micholitzii by many academicians. The cpDNA sequences from 11 populations showed that these very controversial species, C. micholitzii and C. bifida, is paraphyletic and should belong to the same species C. micholitzii. AMOVA analysis showed that the component of among-population within region/species (76.46%) was unexpectedly larger than the among-species/region component (14.97%), which also indicates that there is no justification for recognizing two species as C. micholitzii and C. bifida. This hypothesis was also supported by the geological data, especially the neotectonic history of the indo-china block, which started to move south since Oligocene and cause the geographic isolation of these two groups. Therefore, the most likely explanation to the phenotypic similarities between these two groups may be the retention of ancestral polymorphisms in the paraphyletic group due to incomplete lineage sorting. Furthermore, the similarities may also be ascribed to pollen-mediated gene flow among geographically proximate populations and/or phenotypic convergence under similar selection schemes in the same region. C.micholitzi had the higest genetic diversity (HT = 0.980,) and genetic differentiation (GST = 0.830, NST = 0.915) among the C. micholitzii complex. The high genetic diversity might be attributed to its long evolutionary history, highly diverse habitats. The ineffective mode of seed dispersal and dramatic neotectonic movement in the distribution range of this species could result in the high genetic differentiation. 2. Phylogeographic analysis based on nuclear ribosomal sequences, We sequenced the nrDNA ITS in all 27 populations sampled, 7 haplotypes were identified, among which C. micholitzii had 6, while C. multipinnata, C. longipetiolula and C. debaoensis shared the remaining one. Compared to chloroplast genes, nuclear genes had higher correlation between genetic and geographical distance, but lower interspecies differentiation (54.42% vs 25.24%). Phylogeographical structure of C. micholitzii and C.bifida based on ITS Variation was consistent with the morphology differentiation. This similar in nuclear gene should be ascribed to pollen-mediated gene flow among geographically proximate populations.Long-distance gene flow over the two groups was clearly interrupted, which brought on the nrDNA genetic differenciation between the geographically isolated groups, to a certain extent affected the morphological variation. 3. Interspecies relationships among Cycas micholitzii complex, We analysed chloroplast sequence variation of the atpB-rbcL and psbA-trnH intergenic spacers in 27 populations sampled of C. micholitzii complex, AMOVA analysis showed that the component of among-species/region component (59.21%). However, phylogenic analysis showed that the haplotypes of C. micholitzii complex couldn`t grouped into four clusters closely corresponding to the narrowly defined C. micholitzi, C. multipinnata, C. debaoensis and C. longipetiolula. We concluded that the conflict may result from several factors: firstly incomplete lineage sorting of C. micholitzii; secondly hybridization/introgression of sympatrically cycads, which would be supported by evidence base on nrDNA ITS sequences; thirdly intramolecular recombination in cpDNA of cycads; eventually the neotectonic movement in the distribution range of this 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