Topological incongruence between nuclear and chloroplast DNA trees suggesting hybridization in the urophyllum group of the genus Fagopyrum (Polygonaceae)

We performed phylogenetic analyses of Fagopyrum species in the urophyllum group based on nucleotide sequences of two nuclear genes, FLORICAULA/LEAFY (FLO/LFY) and AGAMOUS (AG), and three segments of chloroplast DNA (cpDNA), rbcL-accD, trnK intron, and trnC-rpoB spacer. The FLO/LFY and AG sequences turned out to be phylogenetically more informative at the intrageneric level than the cpDNA sequences. Congruence among these gene trees, inferred by a maximum-likelihood (ML) method, demonstrated that topologies were partially incongruent between the nuclear and chloroplast DNA phylogenies. The nuclear DNA sequence data supported a monophyletic relation of F. statice, F. gilesii, and F. jinshaense, whereas the former two species formed another monophyletic relation with the F. capillatum-F. gracilipes-F. gracilipedoides-F. rubifolium clade excluding F. jinshaense in the synthetic cpDNA phylogeny. In addition, two divergent sequences of FLO/LFY were found in F. rubifolium (tetraploid). One of these was sister to F. gracilipedoides and another was sister to F. statice, and a monophyletic relation of these two genes was rejected by a bootstrap analysis. These results suggest that hybridization may have occurred during diversification of Fagopyrum species in the urophyllum group, and that F. rubifolium is possibly allotetraploid species.     

Species relationships in Fagopyrum revealed by PCR-based DNA fingerprinting

Random amplified polymorphic DNA (RAPD) markers were used to distinguish between 28 different accessions belonging to 14 species and two sub-species of Fagopyrum. Of the 75 random 10-mer primers tested, only 19 generated robust, easily interpretable amplification products. A total of 364 bands were observed with an average of 19.15 bands per primer, of which 99.45% were polymorphic. Primer OPN-08 produced the maximum number of fragments and UBC-183 produced the minimum number of fragments. The data were utilized to elucidate genetic relationships among 14 species and two sub-species of Fagopyrum. Cluster analysis using the unweighted paired group method of arithmetic means (UPGMA) showed four main clusters, two each of the cymosum and urophyllum groups. The results showed that Fagopyrum tataricum is closer to its wild ancestor F. tataricum ssp. potanini Batalin, closely followed by Fagopyrum giganteum. Cultivated common buckwheat ( Fagopyrum esculentum) showed affinity with its putative wild ancestor F. esculentum ssp. ancestrale and the other closely related diploid species Fagopyrum homotropicum. In the urophyllum group, Fagopyrum macrocarpum and Fagopyrum pleioramosum formed one cluster, whereas Fagopyrum capillatum, Fagopyrum gracilipes and Fagopyrum gilessii clustered separately. Except for a few cases, our results correspond with previously reported studies on Fagopyrum using the isozyme, RFLP and RAPD methods. Species-diagnostic amplification products specific to some species in the cymosum and urophyllum groups were identified. Our results show that RAPDs can be successfully used to analyze species relationships in Fagopyrum and also for constructing linkage maps.     

荞麦属种间13S球蛋白基因序列比较研究

荞麦13S球蛋白是荞麦种子中的一类主要贮藏蛋白。本研究选用荞麦属植物甜荞栽培种及其野生类型、苦荞栽培种及其野生类型、毛野荞、左贡野荞、细柄野荞和硬枝万年荞6个种共44份材料,进行PCR特异性扩增、测序得到荞麦13S球蛋白基因的保守片段序列。对序列进行差异分析,结果发现44份供试材料13S球蛋白基因片段的285个排列位点中不变位点为24个,多态性位点S为261个(含简约信息位点数198个和单型可变位点63个),序列总突变位点Eta为503个。野生甜荞种内13S球蛋白基因序列差异明显高于栽培甜荞,但野生苦荞种内13S球蛋白基因序列差异仅稍高于栽培苦荞。推测其一方面可能与繁殖方式有关,另一方面可能与荞麦驯化过程中通常只有少数野生型群体被驯化有关。系统聚类分析发现栽培甜荞与野甜荞亲缘关系近,与左贡野荞亲缘关系次之;栽培苦荞与野苦荞亲缘关系近,与毛野荞亲缘关系次之;细柄野荞和硬枝万年荞的13S蛋白基因片段序列差异较小,说明其亲缘关系较近。上述结果为荞麦属种间遗传多样性与进化关系研究提供了理论依据。     

Intra- and interspecific phylogeny of wild Fagopyrum (Polygonaceae) species based on nucleotide sequences of noncoding regions in chloroplast DNA

The intra- and interspecific phylogeny of Fagopyrum (Polygonaceae) species was studied using nucleotide sequence data from two noncoding regions in chloroplast DNA, the trnK (UUU) intron and the trnC (GCA)-rpoB spacer. Thirty-seven accessions of ten species and two unidentified samples in the urophyllum group of Fagopyrum were analyzed. Both of the studied regions showed high variability, including nucleotide substitutions, insertion/deletions, and inversions. Separate parsimony analyses of the two regions generated phylogenies that were largely consistent with each other. A single most parsimonious tree derived from the combined data of the two regions suggested that (1) either F. statice or F. leptopodum was derived from the ancestor more than once, (2) F. gracilipes, a tetraploid species, has recently been derived from diploid ancestor and rapidly spread out to its present distribution areas, and (3) F. pleioramosum, F. macrocarpum, and F. callianthum, three newly discovered species endemic to the upper Min River valley, differentiated from their common ancestral species in the present distribution area.     

Two new Fagopyrum (Polygonaceae) species,F. gracilipedoides and F. jinshaense from Yunnan,China

Two new Fagopyrum (Polygonaceae) species, F. gracilipedoides and F. jinshaense, are described. Fagopyrum gracilipedoides was only found at Baoshan village, Lijiang district, Yunnan province, China. This species resembles the weedy species, F. gracilipes in morphology but they differ in both mating system and ploidy level; F. gracilipedoides is a heterostylous self-incompatible diploid species (2n = 16), whereas F. gracilipes is a self-compatible tetraploid species (2n = 32). Fagopyrum jinshaense was found along the Jinsha River valley near the border of Sichuan, Yunnan, and Tibet in China. Fagopyrum jinshaense is morphologically similar to F. gilesii, but they differ in the morphology of their inflorescences. Fagopyrum jinshaense has long spike-like inflorescences, whereas F. gilesii has a compact head-like one. Both F. jinshaense and F. gilesii are self-incompatible with heterostylous flowers and are diploid. Interspecific crosses between the two new species and already known species in the urophyllum group of Fagopyrum resulted in the production of self- and cross-sterile hybrids in the species combinations attempted. These results indicated that both new species are reproductively isolated from other Fagopyrum species. Molecular phylogenetic analysis based on the nucleotide sequence of the trnK gene intron in chloroplast DNA revealed the following points: 1) F. gracilipedoides, F. rubifolium and F. gracilipes / F. capillatum showed a trifurcating relationship and 2) F. jinshaense formed a clade with F. pleioramosum, F. callanthum, and F. macrocarpum, and was only distantly related to F. gilesii. In the clade of F. capillatum, F. gracilipes, F. gracilipedoides and F. rubifolium, the breakdown of self-incompatibility accompanying genome duplication seems to have occurred twice independently.     

Phylogenetic relationship of four new species related to southwestern Sichuan Fagopyrum based on morphological and molecular characterization

Background and aimsRecently, four wild Fagopyrum species, Fagopyrum crispatifolium J. L. Liu, Fagopyrum pugense T. Yu, Fagopyrum qiangcai D. Q. Bai and Fagopyrum wenchuanense J. R. Shao, have been identified and described based on their morphological characters. This study investigates the phylogenetic relationship, nucleotide sequence polymorphisms of internal transcribed spacers (ITSs) and the maturase K (matK) gene within four wild species related to western Sichuan buckwheat. F. wenchuanense is closely related to Fagopyrum gracilipes while F. qiangcai is closely related to Fagopyrum esculentum based on their morphological differences. However, F. wenchuanense is more closely related to Fagopyrum cymosum and F. qiangcai is closer to Fagopyrum lineare and Fagopyrum leptopodum from the viewpoint of the ITS, and matK analysis. In addition, F. gracilipes is closer to F. pugense and Fagopyrum crispatofolium than to F. qiangcai. F. wenchuanense belongs to the cymosum group, while F. qiangcai, F. pugense and F. crispatifolium are classified into the urophyllum group based on their morphological and molecular analysis. Conducting morphological and molecular studies provide a better understanding of evolutionary mechanisms and genetic relationships of cultivated and wild buckwheat in western Sichuan, China.     

Genetic divergence and reproductive isolation in the Ochthebius (Calobius) complex (Coleoptera: Hydraenidae)

The reproductive isolation in hydrenid beetles of the Ochthebius complex was studied by analysing gene exchange in natural populations of O. quadricollis, Ochthebius sp. A and O. brevicollis steinbuehleri collected along the Mediterranean coasts. The ranges of these three species are largely allopatric, but sympatric areas were detected between contiguous taxa, ie, O. quadricollis and Ochthebius sp. A; Ochthebius sp. A and O. b. steinbuehleri. Three levels of reproductive isolation and genetic divergence were observed. One level involves extensive intraspecific genetic divergence within the biological species O. quadricollis, Ochthebius sp. A and O. brevicollis, associated with both physical barriers (eg, sea and sand stretches) and the low dispersal capacity of larvae and adults. The finding of transitional samples between the most differentiated population groups should indicate, however, that there is still some gene flow between the populations of the three taxa. Another level is found between Ochthebius sp. A and O. b. steinbuehleri, whose gene pools appear to be fairly distinct in spite of the fact that reproductive isolation is still incomplete: in their few syntopic sites, some F1 hybrids appeared indeed to have lower fitness, since backcrosses or recombinant genotypes were never observed. The final level in the evolution of reproductive isolation (full reproductive isolation) has been achieved by the species O. quadricollis and Ochthebius sp. A. No F1 or F(n) hybrids, nor backcrosses were found in their sympatric areas. The relative importance of ecological factors and evolutionary forces in the prevention of gene exchange between taxa are discussed.     

Global phylogeography of a cryptic copepod species complex and reproductive isolation between genetically proximate "populations"

The copepod Eurytemora affinis has a broad geographic range within the Northern Hemisphere, inhabiting coastal regions of North America, Asia, and Europe. A phylogenetic approach was used to determine levels of genetic differentiation among populations of this species, and interpopulation crosses were performed to determine reproductive compatibility. DNA sequences from two mitochondrial genes, large subunit (16S) rRNA (450 bp) and cytochrome oxidase I (COI, 652 bp), were obtained from 38 populations spanning most of the species range and from two congeneric species, E. americana and E. herdmani. Phylogenetic analysis revealed a polytomy of highly divergent clades with maximum sequence divergences of 10% in 16S rRNA and 19% in COI. A power test (difference of a proportion) revealed that amount of sequence data collected was sufficient for resolving speciation events occurring at intervals greater than 300,000 years, but insufficient for determining whether speciation events were approximately simultaneous. Geographic and genetic distances were not correlated (Mantel's test; r = 0.023, P = 0.25), suggesting that populations had not differentiated through gradual isolation by distance. At finer spatial scales, there was almost no sharing of mtDNA haplotypes among proximate populations, indicating little genetic exchange even between nearby sites. Interpopulation crosses demonstrated reproductive incompatibility among genetically distinct populations, including those that were sympatric. Most notably, two geographically distant (4000 km) but genetically proximate (0.96% 16S, 0.15% COI) populations exhibited asymmetric reproductive isolation at the F2 generation. Large genetic divergences and reproductive isolation indicate that the morphologically conservative E. affinis constitutes a sibling species complex. Reproductive isolation between genetically proximate populations underscores the importance of using multiple measures to examine patterns of speciation.     

POSTZYGOTIC ISOLATION OVER MULTIPLE GENERATIONS OF HYBRID DESCENDENTS IN A NATURAL HYBRID ZONE: HOW WELL DO SINGLE‐GENERATION ESTIMATES REFLECT REPRODUCTIVE ISOLATION?

Understanding speciation depends on an accurate assessment of the reproductive barriers separating newly diverged populations. In several taxonomic groups, prezygotic barriers, especially preferences for conspecific mates, are thought to play the dominant role in speciation. However, the importance of postzygotic barriers (i.e., low fitness of hybrid offspring) may be widely underestimated. In this study, we examined how well the widely used proxy of postzygotic isolation (reproductive output of F₁ hybrids) reflects the long‐term fitness consequences of hybridization between two closely related species of birds. Using 40 species‐specific single nucleotide polymorphism (SNP) markers, we genotyped a mixed population of collared and pied flycatchers (Ficedula albicollis and F. hypoleuca) to identify grand‐ and great grand‐offspring from interspecific crosses to derive an accurate, multigeneration estimate of postzygotic isolation. Two independent estimates of fitness show that hybridization results in 2.4% and 2.7% of the number of descendents typical of conspecific pairing. This postzygotic isolation was considerably stronger than estimates based on F₁ hybrids. Our results demonstrate that, in nature, combined selection against hybrids and backcrossed individuals may result in almost complete postzygotic isolation between two comparatively young species. If these findings are general, postzygotic barriers separating hybridizing populations may be much stronger than previously thought.     

How many species are in the genus Batrachuperus? A phylogeographical analysis of the stream salamanders (family Hynobiidae) from southwestern China

Phylogeographical analysis of DNA sequence data has been routinely used to test species boundaries using the monophyly criterion; however, a complementary criterion, reproductive isolation, is often ignored. We used a combination of phylogenetic and population genetic approaches to determine species boundaries among stream salamanders in the genus Batrachuperus . First, cytochrome b sequence data from 174 Batrachuperus individuals, sampled from 78 populations, were used to reconstruct historical relationships within the genus. Second, allozyme data for 14 presumptive nuclear loci, from 463 individuals sampled from 60 populations, were collected and analysed to assess population similarity or disparity, as well as potential reproductive isolation. The DNA sequence data grouped all populations into seven major monophyletic groups, and the allozyme data provided evidence for reproductive isolation among four of the seven groups, thereby supporting the species status of these groups. The allozyme data suggested that two of the other groups share the same gene pool, and therefore belong to a single species. Finally, the allozyme data revealed two reproductively isolated units within the seventh group, which we suggest represents a case of 'budding speciation' based on the DNA gene tree. In total, seven species of the genus Batrachuperus were defined, two of which were previously unknown. The phylogeographical analysis also revealed that vicariance events might have dominated the evolutionary history of this group, but the speciation events might precede the formation of the existing mountain topology. This study demonstrates the importance of including frequency data from multiple nuclear gene loci in determining species boundaries.     

Hybridisation and lack of prezygotic barriers between Phymata pennsylvanica and americana

1. The persistence of both geographical and reproductive boundaries between related species poses a fundamental puzzle in biology. Reproductive interactions between species can have a substantial impact on the maintenance of a boundary, potentially contributing to its collapse (e.g. via hybridisation) or facilitating reproductive isolation (e.g. via reinforcement). 2. The degree to which two parapatric insect species in the genus Phymata are reproductively isolated was evaluated and several mechanisms that could contribute to the maintenance of species boundaries were assessed. 3. Behavioural assays showed no indication of species‐assortative mating, nor any fecundity costs associated with heterospecific mating. Thus, there was no evidence of prezygotic mechanisms of reproductive isolation between the two species. 4.In laboratory crosses, it was found that the two species were indeed capable of producing viable F1 hybrids. Morphologically, these hybrids were phenotypically intermediate to the two parental species, and similar to the phenotypes seen in natural populations thought to occur in a hybrid zone. F1 hybrids did not show reduced viability, although there was some suggestion of ‘hybrid breakdown’, evident from the lower viability observed for progeny of ‘natural hybrids’. 5. Collectively, we show that despite genetically based morphological differences between species, P. americana and pennsylvanica can, and probably do hybridise. More studies are needed to understand the mechanisms that maintain the distinct phenotypes and geographical ranges of these species, despite the considerable potential for introgression.     

Morphologically cryptic biological species within the liverwort Frullania asagrayana

? Premise of the study: The Frullania tamarisci complex includes eight Holarctic liverwort species. One of these, F. asagrayana, is distributed broadly throughout eastern North America from Canada to the Gulf Coast. Preliminary genetic data suggested that the species includes two groups of populations. This study was designed to test whether the two groups are reproductively isolated biological species. ? Methods: Eighty-eight samples from across the range of F. asagrayana, plus 73 samples from one population, were genotyped for 13 microsatellite loci. Sequences for two plastid loci and nrITS were obtained from 13 accessions. Genetic data were analyzed using coalescent models and Bayesian inference. ? Key results: Frullania asagrayana is sequence-invariant at the two plastid loci and ITS2, but two clear groups were resolved by microsatellites. The two groups are largely reproductively isolated, but there is a low level of gene flow from the southern to the northern group. No gene flow was detected in the other direction. A local population was heterogeneous but displayed strong genetic structure. ? Conclusions: The genetic structure of F. asagrayana in eastern North America reflects morphologically cryptic differentiation between reproductively isolated groups of populations, near-panmixis within groups, and clonal propagation at local scales. Reproductive isolation between groups that are invariant at the level of nucleotide sequences shows that caution must be exercised in making taxonomic and evolutionary inferences from reciprocal monophyly (or lack thereof) between putative species.     

Glacial cycles drive rapid divergence of cryptic field vole species

Understanding the factors that contribute to the generation of reproductively isolated forms is a fundamental goal of evolutionary biology. Cryptic species are an especially interesting challenge to study in this context since they lack obvious morphological differentiation that provides clues to adaptive divergence that may drive reproductive isolation. Geographical isolation in refugial areas during glacial cycling is known to be important for generating genetically divergent populations, but its role in the origination of new species is still not fully understood and likely to be situation dependent. We combine analysis of 35,434 single‐nucleotide polymorphisms (SNPs) with environmental niche modeling (ENM) to investigate genomic and ecological divergence in three cryptic species formerly classified as the field vole (Microtus agrestis). The SNPs demonstrate high genomic divergence (pairwise F_ST values of 0.45–0.72) and little evidence of gene flow among the three field vole cryptic species, and we argue that genetic drift may have been a particularly important mechanism for divergence in the group. The ENM reveals three areas as potential glacial refugia for the cryptic species and differing climatic niches, although with spatial overlap between species pairs. This evidence underscores the role that glacial cycling has in promoting genetic differentiation and reproductive isolation by subdivision into disjunct distributions at glacial maxima in areas relatively close to ice sheets. Future investigation of the intrinsic barriers to gene flow between the field vole cryptic species is required to fully assess the mechanisms that contribute to reproductive isolation. In addition, the Portuguese field vole (M. rozianus) shows a high inbreeding coefficient and a restricted climatic niche, and warrants investigation into its conservation status.     

荞麦及其野生种遗传多样性分析

荞麦起源于我国西南地区,该地区分布有大量荞麦地方品种和野生近缘种。本研究利用SSR分子标记,对从我国西南地区收集的81份荞麦及其野生资源进行遗传多样性分析。结果显示,利用19对SSR引物共检测出84个等位基因,每对SSR引物平均扩增出4.421个等位基因,19对SSR引物的平均Shannon's信息指数为0.985,平均PIC为0.478。81份荞麦及其野生资源的相似系数范围为0.500~1.000,分析发现大粒组荞麦种(甜荞及其近缘种、苦荞及小米荞、金荞)与小粒组硬枝万年荞亲缘关系比较近。通过聚类分析在遗传相似系数为0.732时,可将81份荞麦种质分为4个类群,第Ⅰ类由小粒组齿翅野荞、细柄野荞、小野荞麦、疏穗小野荞麦和硬枝万年荞组成;第Ⅱ类由甜荞和甜荞近缘种组成;第Ⅲ类都是由金荞组成;第Ⅳ类是由苦荞和小米荞组成。在遗传系数为0.920时,小粒组荞麦种可以明显区分出疏穗小野荞麦、硬枝万年荞、齿翅野荞及其细柄野荞。研究表明,19对SSR引物多态性较高,能较好反应荞麦及其野生种质的遗传多样性,本研究的结果为荞麦属种之间的亲缘关系分析和荞麦起源进化研究提供科学依据。     

The Role of Adaptation to Host Plants in the Evolution of Reproductive Isolation: Negative Evidence from Tetranychus Urticae Koch

Reproductive isolation between demes of a phytophagous arthropod population that use different host plant species could evolve in two different ways. First, adaptation to different host species might result in reproductive isolation as a pleiotropic by-product. Second, if adaptation to one host species strongly reduces fitness on others, selection could favour mechanisms, such as host fidelity and assortative mating, that restrict gene flow between host-adapted demes. A laboratory selection experiment on the broadly polyphagous spider mite Tetranychus urticae gave information on these possibilities. A population allowed to adapt to tomato plants showed increased survival, development rate and fecundity on tomato relative to the base population from which it was derived. In spite of the large difference between the tomato-adapted and base populations in performance on tomato plants, the two populations showed no evidence of reproductive isolation, as measured by the hatching rate of eggs laid by F1 hybrids between the lines. Furthermore, a genetically variable population formed by hybridizing the tomato-adapted and base populations did not show evidence for a decline in ability to survive on tomato after more than ten generations of mass rearing on lima bean, indicating that tomato-adapted genotypes suffered little or no selective disadvantage on bean. These results give no support for the role of host plants in the evolution of reproductive isolation in T. urticae.     

浅析物种概念的演变历史

本文是一篇关于物种概念演变的简述。生物学家用不同的方法或标准划分物种, 就形成了不同的物种概念, 如生物学物种、形态学物种、生态学物种、进化物种、系统发生或支序物种, 或它们的组合, 等等。它们都揭示了物种属性的特定侧面, 都是不同物种客观存在的真实反映, 但都无法令所有人满意。对真核生物来说, 无论它们在形态上的差别有多大, 生殖隔离(不能产生可育的后代)应该是两个群体能否真正分化成不同物种的关键, 这种隔离机制可以是地理的、行为的或其他方式; 而生殖隔离总会伴随着一些形态或遗传上的变化, 虽然这些特征可能与生殖隔离本身并无多大关系, 但往往成为分类学家或分子进化生物学家区分种的依据,对已经灭绝的化石物种来说, 生殖隔离的物种划分方式就无能为力了。如何准确定义一个物种依然充满着矛盾, 因为基于生殖隔离的物种概念不实用, 而实用的物种概念(如形态学物种)又被认为是人为的。     

Morphological characteristics of fruits of Fagopyrum (Polygonaceae) from China

Macro- and micro-morphological characteristics of fruits in eight species and one variety of the genus Fagopyrum Mill. (Polygonaceae) from China were observed under stereoscope and scanning electron microscope(SEM). Based on the results, the fruits of the species studied are divided into type Ⅰ , Ⅱ and Ⅲ. The fruits of type Ⅰ are triangular-pyramidal; their surface are rugosely reticulate, neither smooth nor shiny. Two species, F. tataricum and F. dibotrys have this fruit type. Those of type Ⅱ are ovoid-triangular-pyramidal; their surface are smooth and shiny, and striately reticulate. Three species, F. esculentum, F. statice and F. lineare, have this fruit type. In type Ⅲ, the fruits are ovoid-triangular-pyramidal; their surface are smooth and shiny, and covered with many warty grains and sparsely finely striate. F. urophyllum, F. gracilipes, F. leptopodum var. leptopodum, and F. leptopodum var. grossii have this fruit type. Judging from the morphological characteristics of fruits, F. dibotrys might be more closely related to F. tataricumthan to F. esculentum.     

西南地区硬枝野荞麦(Fagopyrum urophyllum)居群的遗传多样性研究

采用等位酶电泳技术了云南省中北部昆明、富民、宾川3县（市）及四川省西南布拖县的硬枝野荞麦（Fagopyrum urophyllum)6个天然居群的遗传多样性和分化。硬枝野荞麦居群内维持有较高的遗传多样性,多态位点比率为50．0％,预期杂合度和观察杂合度分别为0．251和0．471。并对硬枝野荞麦（F.urophyllum)与栽培荞麦之间遗传变异作了比较。     

Reappraisal of the generic status of Pteroxygonum (Polygonaceae) on the basis of morphology,anatomy and nrDNA ITS sequence analysi

Gross morphology, fruit anatomy, tepal venation, pollen morphology, chromosome number and ITS sequence of Pteroxygonum Damm. & Diels as well as other related genera (Polygonum, Fallopia, Reynoutria, Fagopyrum, and Antenoron) have been investigated to evaluate the generic status of Pteroxygonum. Pt. giraldii Damm. & Diels has three sharp horns at the base of fruit, which is distinctive among all the genera investigated. Upon observation of fruits under a light microscope (LM), the exocarp of Pt. giraldii is usually thickened and delimited by the rectangular cells with some sporadic undulating lumen, while that of Fagopyrum is thin-walled and isodiametric to rectangular in the cell shape. Analysis of tepal venation was performed under a stereomicroscope, and two types of tepal venation were found in Fagopyrum and Pteroxygonum. The type I is trifid, observed in Pt. giraldii, F. esculentum Moench, F. dibotrys (D. Don) Hara and F. tataricum (L.) Gaertn. The type II, found in F. caudatum (Sam.) A. J. Li, F. urophyllum (Bur. & Franch.) H. Gross and F. gracilipes (Hemsl.) Damm. ex Diels, has the main vein extending from tepal base with some secondary veins. Evidence from tepal venation supports the previous classification in which Fagopyrum can be divided into a large-achene group and a small-achene group. Pollen morphology was investigated under a scanning electron microscope (SEM). The exine ornamentation of Pt. giraldii was finely reticulate with lumina diameter wider than muri width. The exine ornamentation in all the examined Fagopyrum species is, however, prominently sunken punctuate. The phylogenetic analysis of nuclear ribosomal DNA (nrDNA) ITS sequences in Pteroxygonum and related genera indicated that all the species form a well-supported monophyletic group with two clades. One includes Polygonum sect. Avicularia Meisn., genus Fallopia and genus Reynoutria, and the other consists of other sections of Polygonum, genus Fagopyrum and Pteroxygonum. The latter clade can be divided into two subclades. Fagopyrum species compose the first one, while Pteroxygonum giraldii, species of Polygonum (except sect. Avicularia) and Antenoron form the second one. In consideration of the above evidence, we conclude that Pteroxygonum is an independent genus in tribe Persicarieae, and should not be merged into the genus Fagopyrum.     

对翼蓼(蓼科)属级位置的重新探讨

通过对翼蓼Pteroxygonum giraldii Damm. &; Diels及相关属(蓼属Polygonum、何首乌属Fallopia、虎杖属Reynoutria、荞麦属Fagopyrum和金线草属Antenoron)的形态观察、果实解剖学观察、花被片脉序观察、花粉形态、核型分析, 以及ITS序列的分析确定了翼蓼和荞麦F. esculentum Moench较远的亲缘关系。其中我们发现翼蓼果实基部有三个角状物明显不同于其他属果实的形态特征。翼蓼外果皮明显加厚, 并有零星散布的波状内腔, 而荞麦的外果皮很薄, 细胞不等径, 中果皮极厚。以上证据证明了翼蓼与荞麦属亲缘关系较远。在观察荞麦属和翼蓼的花被片脉络时发现了两种不同的脉序类型, 符合将荞麦属分为两个组的划分。翼蓼花被片脉序为三出状, 支持将翼蓼归为Persicarieae族。对翼蓼及荞麦属植物的花粉进行比较后, 发现荞麦属植物的花粉网孔有明显的内凹穿孔而翼蓼却没有, 结果表明二者亲缘关系较远。通过对nrDNA ITS区域序列分析得出翼蓼及相关属为一个单系类群, 含有两个稳定的分支: 第一个分支由蓼属(萹蓄组sect. Avicularia)、何首乌属、虎杖属的植物组成, 第二个分支由蓼属(刺蓼组sect. Echinocaulon、蓼组sect. Polygonum、分叉蓼组sect. Aconogonon、拳参组sect. Bistorta、翼蓼和荞麦属植物组成。同时第二个分支又分成了两个亚分支, 蓼属(刺蓼组、蓼组、分叉蓼组、拳参组)和翼蓼属Pteroxygonum植物属于第一个亚支而荞麦属植物属于第二个亚支。结果支持翼蓼不属于荞麦属的范畴。实验结果显示翼蓼是个单型属, 属于Persicarieae族。