Systematic Of Genus Pleurospermum In SiChuan Of China

Pleurospermum Hoffmann belongs to tribe Smyrnieae of subfamily Apioideae, Apiaceae. It comprises about 80 species, mainly distributed in Northern Asia and Western Europe with a high concentration in the alpine areas of Mts. Himalayas. 32 species together with 2 varieties were recorded in Flora of China, found in the southwest, northwest and northeast provinces of China. 25 species among them are endemic to Hengduan Mountains in Southwest China. Many plants of this genus have been utilized as traditional medicine in China and thus are economically valuable. Existing researches mainly focus on the chemical constituents of Pleurospermum plants, and few taxonomic and systematic researches were reported. Taxonomy of this genus has always been problematic both at the intrageneric and infrageneric levels, and study on evolution of this genus is absent. In this thesis, leaf epidermis, pollen morphology, karyology and molecular phylogeny of Pleurospermum were investigated in order to discuss the taxonomy and systematics of this genus as well as to explore the origin and evolution of it.Micromorphological characters of leaf epidermis in 5 species (6 populations) from Hengduan Mts. were examined using light microscopy (LM). Foliar trichome are absent in all the 5 species. Leaf epidermal cells are irregular or polygonal in shape, usually irregular. Stomatal apparatus are found on both adaxial and abaxial epidermis of P. hookeri and P. franehetianum, and are only observed in the abaxial epidermis of P.davidii, P. decurrens and P. wrightianum. The stomatal apparatuses are all anomocytic in the 5 species.Pollen morphology of 6 species of Pleurospermum under light microscopy (LM) and scanning electron microscopy (SEM) were examined and first reported in this thesis. It is shown that pollen characteristics of Pleurospermum are primitive compared to other species in Apiaceae, e.g. the ratio of polar axie to equator axle (P/E) no more than 2, equator protrusive, germinal furrows extending almost to pole, exine thickened at furrow edges and pore edges. Interspecific variations exhibit in terms of equator view, polar view and exine exolamelle. Pollen morphological characteristics indicate that Pleurospermum is a relatively primitive genus in Apiaceae and the infrageneric diversification is not prominent. It is concluded that there is an evolutionary trend of pollen morphology from rhomboidal type to retangular type in Pleurospermum considering the plant morphology and their distribution.Chorosomal numbers of 4 Pleurospermum species were counted and their karyotypes were observed. There are two different chromosomal base numbers within the 4 species, i.e. P. hookeri 2n=2x=22, P. franehetianum, P. decurrens and P. davidii 2n=2x=18. The difference of chromosomal base number indicates that plants of Pleurospermum have at least two different origins and their evolutionary paths are different accordingly. All the chromosomal numbers and karyotypes were first reported here.Internal transcribed sequences (ITS) of ribosomal DNA were analyzed to reconstruct the phologeny of Pleurospermum and its related genera using the maximum parsimony, neighboring-joint and maximum likelihood methods in PAUP4.0b10, respectively. All the results show that Pleurospermum is polyphyletic. The 6 species of Pleurospermum involved in this research cluster into two clades. One clade is made up of P. hookeri and P. yunnanense which are sister groups to each other, and this clade is shown close to the clade of Chaerophyllum+Osmorhiza+Oreomyrrhis. The other clade is the monophyletic group comprising P. franehetianum, P. foetens, P. decurrens and P. uralense with high bootstrap support. Evidences from ITS show that infrageneric divergence exists within Pleurospermum. It is concluded together with the karyological evidences that there are at least two origins in Pleurospermum. P. hookeri represents the clade with chromosomal number 2n=2x=22, while P. franehetianum represents the other clade with chromosomal number 2n=2x=18.In this article, we study the distribution of Pleurospermum Hoffmann in China, according the partition vegetation flora from Wu Zhengyi.The results indicated that most of the Pleurospermum Hoffmann in China distribute in the Hengduan mountains and the circumference of high altitude. In this region, we think that Sichuan is one of the diversity centers.Finally in the present paper, based mainly on morphological characteristics, especially the karyology and molecular systematics, combined with reference to cladistic analysis results and the results of experiments, a conclusion is that Pleurospermum H. in Sichuan can be divided into the following 2sections—Sect. Angustialae and Sect. Latialae. Sect. Angustialae is the most advanced one.The taxonomic arrangement is reviewed; The genus of Pleurospermum Hoffmann and the nearly relationship genus are closing to each other in their morphous. The taxonomy is complicated.It is not monophyly according the research of cytology and molecule. In this region, we think that the circumscription of this genus can be abbreviated.