Study On Micromorphological Features And Classification Of Rhododendron In Southwest Sichuan

Rhododendron not only widely distributed, but also had large differentiation and abundant morphological variation. So many gradient types in Rhododendron made identification and classification work difficult, so that different opinions on Rhododendron classification system were given by many taxonomists in the study on traditional morphological classification. In order to use wild rhododendron resources reasonably, accurate classification system should be formulate as soon as possible. Leaves, leaf midribs and petioles of19wild rhododendrons collected, including4subspecies grade materials, from the mountainous region of Southwest Sichuan were observed and compared by microscopy techniques at cytological level. Their microscopic features were also analyzed, including interspecific variation analysis, cluster analysis and principle component analysis. How much24microscopic characters played a part in Rhododendron classification were evaluated. The relationships being exsitence in different classification degree were discussed. Main results and conclusions were given as follows:(1)Subgen. Hymenanthes and Subgen. Rhododendron had distinctive micro-morphological features respectively, so this study supported H.Sleumer’s taxonomy onto these two subgenus division.(2)Based on the numerical taxonomy of microscopic features was applicable to the classification of Rhododendron. R cluster analysis results showed that:there were different degree correlations between taxonomic character; Principal component analysis results showed that:not more taxonomic characters were selected, better result could be reached, so attention should be paid to select important characters.Scale or no-scale was significant feature, while stomatal density for Rhododendron classification had little significance.(3)Subgen. Hymenanthes without scale is original taxa of rhododendron, while Subgen. Rhododendron with scale is evolutionary taxa. The vascular bundles type of both two subgenus are amphicribral vascular.(4)A kind of specific ultrastructure different from other rhododendrons was found on Rhododendron galactinum’s leaf surface. This structure is covered by fur which is under the leaves, appearing a single or twin circular hole next door, some holes with irregular shape secreta, this is a kind of external secretory structures, speculating nectary or secretory epidermis. Whether it has secretory structure or not and which type of secretory structure it was have certain systematic significance in Rhododendron classification.(5)Subsect. Fortunea and Subsect. Falconera have close phylogenetic relationship, species belonged to two subsections were gotten together in Q cluster.(6)Complex epidermal layers of leaves with the specificity of the subspecies was the basis of R. decorum subdivided into subspecies, but lower epidermis cutin shape was not, it could be used to evaluate its ecological adaptability of different areas.(7)Based on the study of micromorphological variation, this study compiled retrieval table of micro morphological of8rhododendrons characteristics and determined their origins and phylogenetic relationships.(8)96pictures of microscopic structures for comparative anatomy of Subgen. Hymenanthes and Subgen. Rhododendron were provided, which enriched the content of alpine rhododendron classification.(9) R. ploylelis and R. dendrocharis were separated successfully based on the micromorpholoycal features of tender stems firstly, which provided a new idea of the rhododendron paraffin section’s material selection.