Taxonomic Studies On A New Species(Aster Saxicola)and One Of Its Related Taxa(A.ageratoides Var.micranthus)

Southwest China is the distribution center of domestic Aster s.s.However,some species of Aster have not been fully collected and studied or some species have been recorded with uncertain or wrong taxonomic status due to the remote location,inconvenient transportation and difficulty in collecting in the wild in this area.Aster saxicola W.P.Li & Z.Li,a new unrecorded species of Aster,whose taxonomic,cytological,molecular,and ecological research was involved in this paper.At the same time,Aster ageratoides var.micranthus Ling,who is closely related to A.saxicola,was studied in a new and comprehensive way by means of multidisciplinary methods.The following results were obtained.1.Taxonomic study of a new taxa(Aster saxicola)Morphological comparisons showed that A.saxicola is similar to Aster oliganthus W.P.Li & Z.Li,but it can be distinguished by purple abaxial surface of the lower and middle cauline leaves,cordate-ovate basal leaves with strigose hairs,outer 3-seriate phyllaries with purple or purplish apex,9-14 ray florets and 10-18 disk florets.Leaf epidermis study showed that the upper epidermal cells of A.saxicola are irregular in shape and the anticlinal wall is sinuolate.The average number of stomatal apparatus in the lower epidermis is 7.12,and its stomatal apparatus is ellipse-subcircular with sinuate anticlinal wall.Cytological result showed that the new species is diploid with its karyotype formula 2n = 2x = 18 = 16 m + 2sm.Phylogentic analyses based on nrDNA ITS,ETS and plastid trnL-F DNA sequence data support that it is a distinct species with high support and it is sister to varietas of Aster ageratoides.The multidisciplinary evidence indicates that A.saxicola that belongs to Ser.Ageratoides Kitam.is a new species of Aster.And named it Aster saxicola W.P.Li & Z.Li according to its habitat feature.2.Preliminary Studies on Ecology of Aster saxicolaWith fewer than 250 plants,the new taxon is listed as “EN endangered” according to the IUCN endangered list criterion(2001)based on my field research findings.In order to find out the cause of endangered species,the author conducted a quadrat survey and morphological and anatomical research.The reasons for A.saxicola being in danger might be related to the low seed setting rate,the thin rock soil and its weak competitiveness in the homogenous species.The comparison of anatomical structures of roots,stems,and leaves between the A.saxicola and Aster huangpingensis W.P.Li & Z.Li along river distribute in the same area shows that the conducting tissue,the mechanical tissue and the storage structure such as cortex and pith in root and stem are well developed,and stem cortical cells are rich in chloroplasts that these anatomical features suggest that the new species has adapted to the cliff in water-deficient.A.saxicola may be a new species it has not yet spreaded.Nutrients,water is limited relatively and it is adapted to the cliffs of canyons where it is not common to A.saxicola.These reasons may be why it has only one population.3.A taxonomic revision of Aster ageratoides var.micranthusMorphologically,A.ageratoides var.micranthus is most similar to A oliganthus and A.ageratoides var.gerlachii(Hce)Chang.However var.micranthus is easily distinguished by this independent characteristics including short and thick or absent rhizome,stems that is 60-80 cm high,middle leaves that is linear-lanceolate,oblong or oblong-linear with petiole 0.2-2.5cmb long,phyllaries with green or russetish apex,7-16 ray florets and 8-14 disk florets.Cytological study besed on sampling in multiple field areas showed that var.micranthus is polyploidy complex,including diploid,tetraploid and aneuploid.Moreover,phylogenetic trees based on ITS and ETS sequence suggests that var.micranthus collected from seven samples nested within a highly supported clade(ML=80,PP=1.00),and it is distant from other varieties of Aster ageratoides.The evidence based on morphology,cytology and molecular biology suggested that the variety should be isolated from Aster ageratoides and promoted it into a species,which could be renamed as Aster micranthus(Ling)W.P.Li & Y.C.Xiong.