The taxonomic status of Eupatorium chinese var. oppositofolium and E. glehni (=E. chinense subsp. sachalinense) in E. chinense complex semsu Kitamura has long been controversial. In this paper, the degree of divergence between diploids of these two taxa was examined by means of morphological studies including principal component analysis, the electrophoretic analysis of esterase isozyme variation and observations on habitats. The data obtained through the examinations indicate these two taxa are diverged enough to be recognized as distinct biological species. Since the polyploid E. chinense var. oppositifolium is more or less intermediate in morphology between the two diploid taxa, it is considered to have masked the distinction between the two diploid taxa. Also, electrophoretic evidence suggests that polyploid E. chinense var. oppositifolium is not a hybrid or hybrid derivative with E. glehni as a parental species. Possible origin of polyploid E. chinense var oppositifolium is also discussed.
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