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Journal Article

The Cytotaxonomy of Rheum

T. C. Chin and H. W. Youngken
American Journal of Botany
Vol. 34, No. 8 (Oct., 1947), pp. 401-407
Stable URL: http://www.jstor.org/stable/2437150
Page Count: 7
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The Cytotaxonomy of Rheum
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Abstract

A description is given of the Rheum species used in this investigation. The center of primary origin of the Rheum species appears to be somewhere in the vicinity of the Himalaya Mountains, possibly extending into Central China. Emodin and chrysophanic acid were found to occur in the rhizomes and roots of R. officinale Baill., R. palmatum L., R. palmatum var. tanguticum, and Indian and American grown R. Emodi Wallich. Rhaponticin did not occur in any of the aforementioned except American-grown R. Emodi Wallich. Rhaponticin was found in the rhizomes and roots of R. Rhaponticum L., R. undulatum L., R. compactum L. and in the American grown R. Emodi Wallich. R. Franzenbachii Muent. was found to have only a trace of emodin in the rhizome and roots, but chrysophanic acid and rhaponticin were found to be present. The diploid numbers of chromosomes were found to be 22 for R. Franzenbachii Muent., R. Emodi Wallich and R. undulatum L. and 44 for R. tataricum L., R. compactum L., R. altaicum A. Los. and R. australe D. Don. R. Emodi Wallich shows much larger meiotic chromosomes in comparison with R. Franzenbachii Muent., but there is no apparent difference between these species in the size of mitotic chromosomes. The size difference is limited to meiosis. The comparative morphology of the somatic chromosomes showed that R. palmatum L. and R. Franzenbachii Muent. has each one pair of chromosomes with satellites and R. Emodi Wallich and the 2n R. undulatum L. each has two pairs of chromosomes with satellites. The tetraploid R. undulatum L. has 6 chromosomes with satellites which suggests the existence of two genomes of 11 chromosomes in the genus of Rheum and that this tetraploid form arose by amphidiploidy.

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