The taxonomical revision of the genus erigeron L. (asteraceae) in Turkey

The complex geographical distribution of taxa within the genus Erigeron, the scarcity of reliable morphological characters for systematic purposes, and the occurrence of agamospermy in some taxa have hindered the clarification of relationships within the genus. Consequently, systematic studies on the genus have been conducted regionally rather than globally. In this thesis, the aims were to complete the missing descriptions of taxa naturally distributed in Turkey, to characterize their pollen morphology, to update their distribution data, and to elucidate the phylogenetic relationships of the taxa using nucleotide sequences of the ITS region from nrDNA and the trnL-trnF complex from cpDNA. The study involved fieldwork, visits to domestic and international herbaria, examination of type specimens, as well as morphometric and palynological measurements, followed by statistical analyses of these data. Subsequently, phylogenetic relationships among the taxa were inferred based on ITS and trnL-trnF DNA sequences. The results demonstrated that Erigeron s.l. comprises two genera, Erigeron and Psychrogeton. Within the borders of Turkey, Erigeron is represented by 15 taxa, three of which are endemic, whereas Psychrogeton is represented by two taxa. Palynological data revealed that both genera possess tricolporate and echinate pollen grains; however, the pollen grains of Psychrogeton are prolate-spheroidal, while those of Erigeron are oblate-spheroidal or suboblate. DNA sequence analyses indicated the presence of four main groups within Erigeron. The first group consists of Psychrogeton taxa belonging to the subtribe Asterinae. The second group comprises E. bonariensis and E. sumatrensis (sect. Conyza) together with E. canadensis (sect. Caenotus), previously referred to as Conyza. The third group is formed by the E. karvinskianus–E. annuus clade, supported by both molecular and palynological data. The last group consists of taxa from sect. Trimorpha and sect. Erigeron, which, although clearly separated from the other groups, cannot be distinctly differentiated within themselves. These findings clearly demonstrate that these groups are polyphyletic. Furthermore, during the fieldwork carried out within the scope of this thesis, E. akaydinii Günal & Semiz was described as a species new to science from Bursa Uludağ.