Caelestium, genus novum (Polygonaceae, Polygoneae): evidence based on the results of molecular phylogenetic analyses of tribe Polygoneae, established with consideration of the secondary structure of the ITS rDNA regions
The genus Bactria, recently described to house Atraphaxis ovczinnikovii from the Pamirs and Bactria lazkovii from the Central Tien Shan, may also include Polygonum tianschanicum from the Eastern Tien Shan. In order to re-circumscribe Bactria and to clarify the place of Polygonum tianschanicum in tribe Polygoneae, we performed Maximum Likelihood and Bayesian analyses of combined regions of the plastid genome and ITS1-2 regions of nrDNA for 58 species of tribe Polygoneae, with special attention to the secondary structure of pre-rRNA of the ITS1 and ITS2 loci. In all our analyses, Bactria lazkovii and Polygonum tianschanicum formed a highly supported clade, sister to Bactria ovczinnikovii in the plastid trees, but separate from the latter, as well as from the remaining genera in the ITS-based trees. Details of the secondary structure of pre-rRNA of the ITS1 and ITS2 loci also confirmed the close relationships of Bactria lazkovii and Polygonum tianschanicum, quite different from Bactria ovczinnikovii. Based on the molecular analyses, details of the secondary structure of pre-rRNA of the ITS1 and ITS2 loci, fine morphological distinctions, and distributional data, we propose the new genus Caelestium Yurtseva et Mavrodiev, presumably of hybrid origin, to include C. lazkovii and C. tianschanicum.