A comparison of chromosome characters in three species of Thymus (Lamiaceae) collected in Russia and Mongolian Altai

抄録

Characters of the resting, the mitotic prophase and metaphase chromosomes in three species of Thymus were studied. The species studied had commonly resting chromosomes of the complex chromocenter type and mitotic prophase chromosomes of the proximal type. Thymus mongolicus showed the chromosome numbers of 2n=26 and 27 and T. przewalskii and T. roseus showed the chromosome number of 2n=26. The chromosome number of 2n=26 for T. przewalskii and that of 2n=27 for T. mongolicus were reported here for the first time and that of 2n=26 for T. roseus and T. mongilicus verified the previous reports. The chromosome number of 2n=27 for T. mongolicus seemed to have one B-chromosome as 2n=26+1B with respect to the existence of a peculiar heteropycnotic body at resting stage and high pollen stainability. Three species were commonly placed in the diploid level if the basic chromosome numbers of x=13 was accepted. Their karyotypes at mitotic metaphase were quite similar to each other regarding chromosome sizes, chromosome types according to the centromeric position and mono-modality of chromosome lengths from the longest to the shortest chromosomes except for satellite sizes.