Systematics Of Heracleum L. In Southwest China

Heracleum L. belongs to subtribe Tordyliinae of tribe Peucedaneae, subfamilyApioideae, Apiaceae. It comprises ca. 70 species mainly distributed in temperateareas of Asia and Europe with only 1 species in North America and few in EastAfrica. Caucasus Mountains and Hengduan Mountains are the 2 distribution centreof Heracleum in the world. 29 species together with 4 varieties were recorded inFlora of China, among which 28 species and 2 varieties were found in the area ofHengduan Mountains and 21 species and 2 varieties are endemic to HengduanMountains in Southwest China. Taxonomy of this genus has always beenproblematic both at the intrageneric and infrageneric levels due to the complexity ofits morphology, the general paucity of good herbarium specimens and the inadequacyof historic type material. In this thesis, leaf epidermis, pollen morphology,karyology and molecular phylogeny of SW China Heracleum species wereinvestigated in order to discuss the taxonomy and systematics of this genus as well asto explore the origin and evolution of it.Micromorphological characters of leaf epidermis in 11 Heracleum species (16populations) from Hengduan Mts. were examined using light microscopy (LM) andscanning electron microscopy (SEM). Foliar trichomes were observed on onlyabaxial epidermis in H. acuminatum, on only adaxial epidermis in H. hemsleyanum,H. stenopterum and H. forrestii, and on both sides in other 7 species with diverseshapes. Stomatal apparatus were found on both adaxial and abaxial epidermis of H.dissectum, H. apaensis, H. hemsleyanum and H. stenopterum, and were onlyobserved in the abaxial epidermis of the other 7 species. Leaf epidermal cells areirregular or polygonal in shape, usually irregular. The patterns of anticlinal walls are straight, curved or undulate. The stomatal apparatuses are all anomocytic in the11 species. Outer stomatal rims are nearly smooth or covered with granular,laminar or tuberculate projections, with inner margins nearly smooth, sinuolate orsinuous.Pollcn morphology of 11 Heracleum species was examined under LM andSEM. It is shown that pollens of these specics are all of retangular type andequatorial constricted type, with polar views of 3-splitted round, obtuse triangle ortrianglc. Interspecific variations exhibit in pollen size and exine exolamelle.Morphological characteristics of pollens indicate that Heracleum is a relativelyadvanced genus of Apiaceac in active differentiation, and that all the species areclosely related to each other.Chorosomal numbers of 2 Heracleum species were counted and thcirkaryotypes were analyzed. Chromosomal numbers of the two species are both2n=22. Karyotype of H. candicans is 2A type with the formula as2n=2x=22=12m+6sm+4st, while that of H. hemeslayanum is 1A with the formula as2n=2x=22=2M+4sm+16m (2SAT). It is preliminarily concluded that theTordyliinae species originated in the Caucasus area based on the existing kariological,morphological and geographic datas.Internal transcribed sequences (ITS) of ribosomal DNA of 36 species wereanalyzed to reconstruct the phologeny of Heracleum and its related genera using themaximum parsimony, neighboring-joint and maximum likelihood methods inPAUP4.0b10, respectively. All the results show that Heracleum is polyphyletic andclosely related with Pastinaca, Semenovia, Tetrataenium and Zosima. Evidencesfrom ITS support to place H. apaensis into Angelica and to include the 4 relatedgenera into Heracleum.