Taxonomic Revision Of Astragalus L. Subgenus Pogonophace Bunge (Leguminosae) And A Preliminary Study Of Its Systematic Position

The subgenus Pogonophace (Astragalus, Leguminosae) mainly occurs in the Hengduan Mountains and Qinghai-Xizang Plateau. Most species in this subgenus are very local and are taxonomically poorly known due to the lacking of field observations and the scantiness of herbarium specimens. In addition, the scope of Pogonophace and its systematic position are not clear, and remain to be studied. In this study, the taxonomy on the species of Pogonophace from China was revised. The phylogenetic relationships of this subgenus and its related groups were also addressed based on evidence from morphology and molecular systematics.1. Taxonomic revisionLiterature survey, herbarium study, and field observation of species within Pogonophace have been done in this study. Morphological variations were studied with special reference to their scopes of variations within and between populations. The lengths of the stems and flowers, and the shape of fruits are reliable diagnostic characteristics. Moreover, the pubescence of the stems and leaflets, the shape of the leaflets and bracteole, and the color of flowers are also useful characteristics for the delimitation of species within this subgenus.In this study, twenty-three species and six varieties are recognized in China. Seven species are separated from Pogonophace, and nine species are treated as synonymies. Two previously recognized species, A. yatungensis and A. monanthus, are synonymies of A. donianus, which is newly recorded in China. The identity of A. angustifoliolatus, A. dolichochaete, A. lichiangensis and A. camptodontus wasclarified. Description, the information of the distribution sites and a key to the species in China are also given.2. MicromorphologyThe styles of Pogonophace were investigated under the scanning electron microscope (SEM) with respect to morphology at different developmental stages and at maturity. The results revealed that the commonly used term "bearded stigma" is an inaccurate characterization to some species of this subgenus. For example, the trichomes of them are initiated from the top of the style, but the stigma is glabrous. In addition, the trichomes of these species are erect and upwardly pointed. This is the essential feature of the pollen brush. Other characteristics correlated with the pollen brush also occur in these species. Because the pollen brush is the diagnostic feature of subtribe Coluteinae, it suggests that the species with this characteristic in Pogonophace should be separated from Astragalus and treated as a genus of Coluteinae, and Phyllolobium is the suitable name to this genus.3. Leaf epidermisLight microscope was used to examine foliar epidermal features of eleven species representing the four sections of Pogonophace. The two types of stomatal apparatus, anomocytic and actinocytic, are possessed by each species, while the former is the predominating type. Three types of foliar epidermal cells can be recognized based on the cell shape and its anticlinal wall. The cell shape of observed species in section Sesbanella is anomalus and its anticlinal wall is sinuose. The cell shape of observed species in section Trichostylus is long and narrow, and its anticlinal wall is straight or a little sinuose. The cell shape of observed species in section Phyllolobium and section Bibracteola is round or polygonous and its anticlinal wall is straight. The epidermal cells may provide useful information to the delimitation of Pogonophace and its sections.4. Molecular systematicsThe internal transcribed spacers (ITS) (including ITS1, 5.8S rRNA gene and ITS2) of some species in Pogonophace were sequenced, and analyzed togetherwith other ITS data (from genbank) of fourty-eight species representing Astragalus and twelve related genera. Phylogenetic tree was constructed when Caragana roborovskyi was designated as the outgroup. The results of parsimony analysis suggest that Pogonophace is not a monophyletic group. The species of section Sesbanella and other species of this subgenus are nested within different major clades in the phylogenetic tree. The...