Karyotypes of two endemic species of Asterothamnus Novopokr. (Asteraceae) from South Siberia (Tuva)

The karyotypes of two endemic species such as Asterothamnus heteropappoides and A. poliifolius from South Siberia were studied. Both species were diploids with the chromosome numbers of 2n = 2x = 18. The polyploidy and satellites were not found. For the first time, the chromosome morphology has been studied and the idiograms have been plotted. The chromosome sizes ranged from 6.42 to 4.23 μm for A. heteropappoides and the karyotype formula of 8m + 1sm and that from 5.88 μm to 3.64 μm for A. poliifolius and featuring the karyotype formula of 9m.


Introduction
The genus Asterothamnus Novopokr. belongs to the subtribe Asterinae (Cass.) Dumort. (the tribe Astereae, the family Asteraceae). According to Nesom & Robinson (2007), it includes 13 genera and approximately 270 species. The molecularphylogenetic analysis of the subtribe Asterinae (Li et al., 2012;Korolyuk et al., 2015) states the differentiation of Asiatic taxa into five wellsupported clades. These are the Galatella group with the species of Asian genera Galatella Cass. s. l. and Tripolium Nees.; the groups of species of North American origin; and three groups of allied Eurasian species: (1) the group of typical Eurasian Aster L. (2) the Heteropappus group including Heteropappus Less. and Kalimeris Cass., as well as (3) Asterothamnus group. The monophyletic clade Asterothamnus includes endemic Central Asian species of the genera Asterothamnus and Rhinactinidia Novopokr., several endemic species of Aster from China, and the monotypical genus Arctogeron DC. All the genera mentioned, except for Asterothamnus, contain polyploid taxa. According to the published data, a number of species of the Asteraceae featuring single chromosomes in a chromosome set that may differ morphologically from each other. This can serve as an additional taxonomic marker and reflect evolutionary relations of the allied taxa (Li, 2006). The species belonging to the Asterothamnus group have been less studied cytologically: the chromosome numbers of 2n= 18, which have been reported in the two species of Asterothamnus, are known for two species of Asterothamnus (Krasnikov, Korolyuk, 1995) and those for Arctogeron gramineum (L.) DC. (Rostovtzeva, Ligus, 1978). However, the chromosome morphology has not been studied yet.
Asterothamnus includes seven xerophytic species which are restricted to semi-deserts or dry rocky steppes. Most of the species grow in the territories of Mongolia and China; two species are endemic to Middle Asia (Novopokrovskiy, 1950;Grubov, 1982;Chen et al., 2011). Two species occurring in Siberia, A. heteropappoides Novopokr. and A. poliifolius Novopokr., are endemics to Tyva Republic (Korolyuk, 1997).
The aim of this work is to study karyotypic peculiarities of chromosomes of Siberian A. heteropappoides and A. poliifolius as a part of ongoing revision of the genera of the subtribe Asterinae.

Materials and methods
The plants for the study were collected in the territories of Ovyursky and Tes-Khemsky Regions of the Republic of Tyva. The herbarium samples are stored at the Herbarium of the Central Siberian Botanical Garden SB RAS (NS).
The karyological analysis was made by using root meristem squash preparations from seedlings. Seeds were sprouted in petri dishes on wet sterile sand at 27 °С and light regime providing 16 hours of daylight and eight hours of darkness. The germs were treated in 0.2 % colchicine for two hours and then fixed in a mixture of ethanol-acetic acid (3:1). The chromosomes were stained with aceto-haematoxyline according to Smirnov (1968). Slides were examined under Axioscop-40 microscope. Chromosome analyses were made on 5-10 slides under 100X magnification. The study of karyotypes and their descriptions were made according to Levan et al. (1964). A1 was estimated according to Romero Zarco (1986), and TF % followed Huziwara (1962). Chromosomes and chromosome arm lengths measurement were made by MicroMeasure software environment (Aaron Reeves, USA).
Conclusively, the karyotypes of the species studied were similar in chromosome number and size, as well as no satellites and secondary constrictions. Minor differences were revealed for chromosome morphology. Thus, karyotype formula of A. heteropappoides was 2n = 18 = 8m + 1sm, while that of A. poliifolius was 9m.