Taxonomic Revision Of The Genus Rhododendron (Ericaceae) In Guangdong And Haina

Rhododendron is the largest genus of Ericaceae,with about 1000 Rhododendron species widely distributed in Asia,North America and Europe.Based on a thorough literature survey,39 species and three varieties and 7 species and 1 variety of Rhododendron are recorded from Guangdong and Hainan respectively.Due to the large number of species and complex variation patterns of morphological characters in this genus,the taxonomic status and specific delimitation of many species(especially R.mariae,R.ovatum and their related species)are controversial among different studies.To solve these taxonomic problems,this study intended to complete a preliminary revision of the genus Rhododendron in the two provinces by literature study,specimen examination,field observation and molecular phylogenetic research.The main results are as follows:1.The variation patterns of morphological characters of Rhododendron in two provinces were analyzed and studied.The results showed that the habits,branches(thickness and branching),indumentum types,leaves(texture and growth pattern),flower buds(shape,size,shape of bud scale,position relative to leaf buds),inflorescences(inflorescence type and number of flowers per inflorescence),corollas(shape,color,tube shape),stamens,pistils(ovary shape,cells of ovary),fruits(shape,dehiscence pattern)are relatively stable characters,which are the important morphological classification feature of the species of Rhododendron.Among them,habits,branch thickness,indumentum types,relative position between foliar and floral buds,and fruit shape and dehiscence pattern are also important features for the delimitation of the subgenera of Rhododendron.2.The phylogenetic relationship of some Rhododendron species in Guangdong and Hainan provinces was reconstructed by using chloroplast coding sequences and nr DNA sequences.The main conclusions are:(1)the species discriminating power of these two sequences are too limited to solve the relationship within sections,and that of the 66 chloroplast coding sequence is comparatively higher;(2)the monophyly of subgen.Tsutsusi is supported,and the subgen.Azaleastrum is shown as polyphyletic with the inconsistent phylogenetic position of sect.Azalea and sect.Choniastrum in nr DNA sequence and chloroplast gene analysis;(3)both sect.Tsutsusi and sect.Brachycalyx are monophyletic,and the species with five stamens and those with ten stamens in sect.Tsutsusi may be connected by Rhododendron naamkwuanense;(4)The inconsistent phylogenetic positions in nr DNA sequence and chloroplast gene analysis of some species indicate that hybridization may happen in Rhododendron.3.Based on the results of morphological and phylogenetic studies,the following taxonomic treatments are made:(1)R.subenerve var.nudistylum is raised to the rank of species;(2)a new variety of R.mariae,i.e.,R.mariae var.moi,is described,and R.tingwuense and R.huiyangense are both treated as varieties of R.mariae;(3)R.simiarum var.grandifolium and R.hongkongense are treated as a synonym of R.simiarum and R.ovatum respectively;(4)the lectotype of R.chunii is designated;(5)the descriptions of some species are supplemented and revised.Finally,33 species and three varieties of Rhododendron in Guangdong Province and 8 species in Hainan Province are recognized respectively.