Caelestium (Polygonaceae, Polygoneae), evidence bаsed on morphology

Morphological characters and fruit anatomy were analysed for distinguishing the new genus Caelestium, containing C. lazkovii (= Bactria lazkovii), endemic of the Central Tien Shan (Kyrgyzstan), and C. tianschanicum (= Polygonum tianschanicum), endemic of the Eastern Tien Shan (Xinjiang, China), from the genus Bactria in its updated circumscription, now containing only B. ovczinnikovii, endemic of the Pamir (Tajikistan). The genus Caelestium was established based on the results of molecular analyses and the details of the secondary structure of pre-rRNA of the ITS1 and ITS2 loci, but its morphology is poorly known. The morphological characteristics of Bactria and Caelestium were compared, and the anatomy of fruit was examined for these taxa and some species of Persepolium and Atraphaxis. Caelestium lazkovii and C. tianschanicum share the morphology of their leaf blades, perianth, fruits and styles, but differ in the color of annual shoots, the size of the perianth and fruits. They resemble Bactria ovczinnikovii in their life form, morphology of shoots, ochreas, inflorescences, and sporoderm ornamentation, but differ from the latter in the shape of leaf blades, fruits, and styles, micromorphology of tepals, and exocarp structure. SEM and LM images illustrating morphological characters are provided. The geographic ranges of the taxa are presented on the distribution map. Morphological characteristics distinguishing Caelestium and Bactria from Atraphaxis, Persepolium, and Polygonum are discussed.