Studies On Molecular Systematics Of Genus Polygonum S. Lat And Its Related Taxa From China

The genus of Polygonum L. s. lat. was established by Linnaeus, a swedish taxonomist, in1753. However, this is a controversial and not fully successful taxonomy system and it has remained challengging and problematic for taxonomists in the field to use this classification method. As such, many researchers have tried to subdivide the genus into more natural units at generic and subgeneric levels. It is still debating and inconclusive whetehr or not to use those new classification units due to lack of sufficient and cruical evidence.There are235(or238) species belong to13genera in the family of Polygonaceae recorded in《Flora of China. Those plants are subdivided into two subfamilies (i.e., Polygonoideae and Rumicoideae) based on their morphological characteristics. The tribes of Polygoneae and Atrophaxideae belong to the subfamily of Polygonoideae. The tribe of Polygoneae is subdivided into seven genera, including Koenigia L., Polygonum L., Fallopia Adans., Reynoutria Houtt., Antenoron Rafin., Fagopyrum Mill., and Pteroxygonum Damm. et Diels. However, there are many controversial problems in this classification system. This thesis focuses on the tribe of Polygoneae, attempting to establish a new classification method for those genera.Many researchers have tried to study the classification system of Polygonum genus in China using methods of morphology, pollen morphology, micro-morphology, anatomy, cytology and molecular biology. By doing so they have reached some important conclusions. Plant Molecular systematics applies various experimental methods of molecular biology to obtain all kinds of molecular information and based upon those information to further explore the phylogenetic relationships between different plant taxa and their evolutionary processes and mechanisms involved. This new classification method moves the studies of plant system development and evolution to molecular level. Although plant molecular systematics has been established for only20years, it has led to the most dramatic and important changes in higher-level angiosperm taxonomy that had been established using traditional methods in the past200years and it has provided unparalleled insights into relationships at all levels of plant phylogeny.The sequences of nrDNA ITS and two spacer regions of cpDNA trnL-trnF and atpB-rbcL are widely used in plant molecular systematics studies. Those genetic markers are selected for the studies in this thesis. The experimental samples consist of84species:5-10species from every section of Polygonum s.lat. and the genera in tribe Polygoneae (e.g., Fallopia Adans., Fagopyrum Mill. and Koenigia L. emend Hedberg),1-2species from the satellite genera (e.g.,Reynoutria Houtt., Antenoron Rafin.) and Pteroxygonum Damm. et Diels, as well as1-2species from the genera in the tribe of Atrophaxideae (e.g., Atrophaxsis L., Calligonum L. and Parapteropyrum Damm. et Diels). The out-group (do you mean unrelated group? or control group?) consists of6-7species which are selected from genus Rumex L., Rheum L. and Oxyria Hill in the tribe of Rumiceae Damm. The chromosome DNAs were first extracted from those plants, and then the aforementioned three DNA segments were PCR amplified, and finally sequenced. The three single gene data, two chloroplast segments combination datasets, and three segments combination datasets were calculated to obtain their Maximum Parsimony (MP) trees, Neighbor-joining (NJ) trees with the software PAUP*v.4.0b10. At the same time, the Bayesian inference (BI) trees were calculated with the software MrBayes*v.3.1.2by the plugin imported into the software platform of Geneious4.8.3for above five data matrixes. Then a series of procedures was operated to calculate the divergence time of the important nodes in the software package of BEAST v1.6.2using the method of earliest pollen age scales of genus Polygonum and Rumex as described in the papers listed in the stratum reference.The systematical status of genus Koenigia s.lat. and the relationship between the species within the genus were further studied by calculating the MP, NJ, BI trees and the divergence time of the important nodes as above. Calculations for the MP, NJ, BI trees and divergence times were conducted from a total of82taxa from the close relatives taxa, such as genera of Antenoron, Echinocaulon, Persicaria, Cephalophilon, Aconogonon and Bistorta. By comparing with data from each1-8population samples from the genus of Koenigia s.lat, the main results are acquired as below.The genus Polygonum s.lat. is not a monophyletic group instead of a polyphyletic group; and the sections in this group should be set up as genus units. Some species positions in the genera should be adjusted according to the below suggestions:(1) Polygonum sibiricum should be removed from the genus of Aconogonon and be promoted to the genus of Knorringia Tzvel.(2) Reynoutria and Fallopia have a close genetic relationship, suggesting that they probably came from a same ancestor. It is likely that in the evolution process, one branch is evolved towards the genus of Reynoutria that has an erect stems while the other branch is evolved towards the genus of Fallopia that has either sprawling or twining stems. The results support that they both are a separated genus, i.e., either Reynoutria Houtt. or Fallopia Adans.(3) The results support that Pteroxygonum Damm. et Diels is a status of genus but it is not a single species genus and it should include at least two species: Pteroxygonum giraldii and Fallopia denticulata. As such, Fallopia denticulata should be emended as Pteroxygonum denticulata.(4) The results show that Parapteropyrum tibeticum should be removed from the genus of Parapteropyrum and moved to the genus of Fagopyrum and the annul status of Parapteropyrum. It should be emended as Fagopyrum tibeticum.(5) Polygonum Sect. Aconogonon should be promoted to a status of Aconogonon Reichb.; and Polygonum sibiricum should be removed from the genus of Aconogonon and be moved to the genus of Knorringia. The results also support the classification proposed by Professor Zhou that the genus of Aconogonon should be subdivided into three sections:Aconogonon sect. Polystachyum, Aconogonon sect. Aconogonon and Aconogonon sect. Campanulatum.(6) Polygonum delicatula is a species of Polygonum section Cephalophilon. However, the molecular trees show that it is obviously apart from the Polygonum section Cephalophilon and it should not belong to the genus of Koenigia. Polygonum delicatula appears to be a close relative of the genus of Aconogonon. Interestingly, Polygonum delicatula is always in the same big branch as Aconogonon and Koenigia genus. So it is likely that they came from the same ancestor, and then first evolved into Polygonum delicatula, and further into the genus of Aconogonon. Moreover, some species of Aconogonon might be differentiated into the genus of Koenigia. However, Polygonum delicatula keeps some of the most important characteristics ofKoenigia genus, such as spiny pollen. Also, it has the same distribution area with the species of genus Koenigia. Thus, it should be admitted as a species of Koenigia and it should be emended as Koenigia delicatula (Meisn.) Hara.(7) The results show that Polygonum sect. Persicaria and Polygonum sect. Echinocaulon are a status of genus, i.e., the genus of Persicaria Mill. and the genus of Truellum Houtt. At the same time, Polygonum bungeanum, which is a species of Polygonum section Echinocaulon, should be moved into the genus of Persicaria and it should be emended as Persicaria bungeana (Turcz.) Nakai.(8) The genus of Antenoron is a close relative to the genus of Persicaria Mill. and it has a parallel relationship with the genus of Truellum Houtt. Therefore, Antenoron should not be in the genus of Persicaria. Instead, it should be an independent status, i.e., the genus of Antenoron Rafin.(9) Polygonum delicatula is moved into the genus of Koenigia that was a species of Polygonum section Cephalophilon previously. In addition, Polygonum nepalensis, Polygonum sparsipilosum, Polygonum sparsipilosum var. hubertii, Polygonum cyanandra and Polygonum fertile should also be moved to the genus of Koenigia which were species of Polygonum section Cephalophilon previously. The remaining species constitute the genus of Cephlophilon Spach.(10) Polygonum Sect. Bistorta is undisputedly as a single group, and it should be promoted to the genus of Bistorta Adans.(11) Except for Koenigia delicatula, all the selected species from the genus of Koenigia L. emend Hedberg and two new species (in press) form a monophyletic group. This result indicates that the genus of Koenigia L. emend Hedberg is a natural taxa and that it is a young genus which is derived from some of the ancestors of Aconogonon due to the uplift of the Qinghai-Tibet Plateau and the change of special environment (interior islands of habitats), and then gradually evolved into various species of the genus of Koenigia. The genus of Koenigia L. emend Hedberg contains about8-10species. This genus should be subdivided into three sections:Koenigia sect. Delicatula, Koenigia sect. Forrestii and Koenigia sect. Koenigia.(12) Finally, a new classification system of family Polygonaceae plants from China is established based on the results of molecular phylogenetic tree analyses.