Gene duplications in Eupatorium and their systematic implication

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Eupatorium (Compositae) disjunctly occurs in North America and East Asia. Diploid species of the genus have ten pairs of morphologically differentiated somatic chromosomes and are cytogenotically in diploid or amphidiploid condition. The haploid number 10 is common among many genera in the tribe Eufatorieae and had been regarded as the basic chromosome number of the tribe. This study, however, uncovered that diploid species of Eupatorium (both Asian and American) have extensive duplications of genes encoding seven enzyme species which are routinely examined in enzyme electrophoresis. This result suggests polyploid origin of the genus and also of the tribe Eupatorieae. Using the restriction fragment length polymorphism of chloroplast NA, it is confirmed that the tribe Eupatorieae is derived from the tribe Heliantheae in which haploid chromosome numbers more that ten are prevalent. Thus haploid chromosome number ten prevailing in the tribe Eupatorieae is probably reduced from higher numbers in the tribe Heliantheae. Further study to test this hypothesis is now in progress.