Abstract
A coastal biennial herb, Lysimachia mauritiana, exhibited remarkable intraspecific karyotypic diversity, especially in the Ryukyu Archipelago of Japan (the Ryukyus). The species displayed five chromosome numbers (2n=16, 17, 18, 19, 20) and 18 cytotypes in the Ryukyus alone. Our serial investigations elucidated that: (1) 11 cytotypes on Takarajima Island (Is.) showed the highest intra- and inter-populational cytotype polymorphism in the Ryukyus, (2) a total of 15 cytotypes was recognized and several cytotypes coexisted in every locality on Amamioshima, Kakeromajima and Tokunoshima Is., and (3) closely located two Islands of Amamioshima and Tokunoshima had different dominant cytotypes, 16 (6m) and 18 (6m), respectively. In the present study, to explore whether a similar karyotypic polymorphism exists on their neighbor islands belonging to the Okinawa and the Daito Groups, a total of 610 plants from 51 localities on 10 islands were analyzed karyomorphologically and cytogeographically. As a result, five chromosome numbers (2n=16, 17, 18, 19, 20) and 13 cytotypes were recognized in the areas. Okinawajima Is. was divided into two areas according to cytotype distribution patterns. Northern and western areas facing the East China Sea showed intra- and inter-populational polymorphism in cytotype. By contrast, southern, eastern and northeastern areas facing the Pacific Ocean showed a single cytotype in a locality. In the Daito Group, 20 (4m) TS cytotype with a wide distribution in southern Taiwan was found in Japan for the first time. The cytotype probably descended from currents of southern Taiwan and/or the Philippines.
