Karyotypic analysis of Skimmia japonica (Rutaceae) and related species.

A karyotypic analysis of three species of Skimmia (Rutaceae) in East Asia was performed that examined 88 individuals from 53 localities. Chromosome numbers of S. japonica, S. reevesiana and S. arisanensis were 2n=30, 31, 32 (=30+0-2B), 2n=60 and 2n=60, respectively. The chromosome number of S. arisanensis was reported for the first time. All species had a large chromosome pair or quartet (the first pair or quartet) with a median-submedian centromere in the karyotype. In S. japonica the arm ratio of this first pair was considerably variable and showed a geographical pattern. In the northern half of the distribution range, Sakhalin, Hokkaido, Honshu, Shikoku and part of Kyushu, the arm ratio was 1-1.2, while in the southern half, part of Kyushu, Ryukyu and Taiwan, the arm ratio was very variable and ranged from 1.2 to 2.4. In S. japonica the first pair was sometimes rather heteromorphic; however, the heteromorphism was not related to sex of the plant.