Hybrid origins of Ixeris nakazonei (Asteraceae, Lactuceae) in the Ryukyu Archipelago, Japan: Evidence from molecular data

Abstract

The proposed hybrid origin of Ixeris nakazonei collected in the Ryukyu Archipelago (Okinawajima) and the Atsumi Peninsula (Koijigahama) of central Japan was examined using nuclear DNA (nDNA) and chloroplast DNA (cpDNA) markers. The results indicated that most tetraploids of I. nakazonei (2n = 32) had nDNA of both putative parents, I. debilis (2n = 48) and I. repens (2n = 16). The first tetraploid of I. nakazonei must have arisen directly from interspecific hybridization between I. debilis and I. repens, considering the intermediacy of the chromosome number. All tetraploids on Okinawajima had cpDNA of I. repens, while those in the Atsumi Peninsula had cpDNA of I. debilis, indicating that the tetraploid has at least two independent origins. All hexaploids of I. nakazonei (2n = 48), on the other hand, had cpDNA of I. debilis, but some of the hexaploids had nDNA of both putative parents. Ixeris debilis and I. repens may also be involved in the origin of the hexaploid, although the establishment process of this cytotype is still obscure. Since the hexaploid of I. nakazonei is cytologically indistinguishable from I. debilis, it can backcross with I. debilis. Introgression from diploid I. repens to hexaploid I. debilis mediated by I. nakazonei possibly occurs on Okinawajima. © 2003 The Linnean Society of London.