Abstract
Clerodendrum trichotomum s. lat., under which many infraspecific taxa have been recognized, includes both tetraploid and diploid individuals, although chromosome numbers and geographic variation in ploidy levels have not been investigated in the Japanese archipelago. The geographic distribution of ploidy levels and chloroplast haplotypes of four Japanese taxa of C. trichotomum s. lat., based on chromosome counts, flow cytometry, and genotyping of five microsatellite loci is reported. It was determined that Japanese C. trichotomum var. trichotomum and var. yakusimense are tetraploid (2n = 104), while var. esculentum and C. izuinsulare are diploid (2n = 52). The diploid taxa are distributed only on the southern edge of the Japanese archipelago, while tetraploid C. trichotomum is distributed widely. Such distribution patterns may be formed by temperate forest shrinkage during, and tetraploid expansion after, glacial periods. Thirteen haplotypes were detected, and were divided into the following three clades: (1) Japanese C. trichotomum var. trichotomum and C. izuinsulare, (2) C. trichotomum var. yakusimense and var. esculentum, and (3) Chinese C. trichotomum. Two haplotypes were shared between diploid and tetraploid lineages, suggesting multiple polyploidization events in C. trichotomum s. lat.. Inconsistency between nuclear and chloroplast phylogenetic trees suggests a past inter-lineage hybridization event in C. trichotomum s. lat.
