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Natural Hybridization between Two South American Diploid Species of Andropogon (Gramineae)

F. Galdeano and G. Norrmann
The Journal of the Torrey Botanical Society
Vol. 127, No. 2 (Apr. - Jun., 2000), pp. 101-106
Published by: Torrey Botanical Society
DOI: 10.2307/3088687
Stable URL: http://www.jstor.org/stable/3088687
Page Count: 6
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Natural Hybridization between Two South American Diploid Species of Andropogon (Gramineae)
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Abstract

In two mixed populations of Andropogon selloanus (Hack.) Hack. and A. macrothrix Trin. from northeastern Argentina we found two individuals that were morphologically intermediate between these two taxa. The hypothesis that these individuals were natural hybrids was tested through comparisons with a controlled hybrid obtained from the cross A. selloanus x A. macrothrix. The results show that there are neither morphological, nor cytological, nor reproductive differences among intermediate individuals and the controlled hybrid; therefore they deserve to be regarded as products of natural hybridization. Meiotic chromosome behavior in the hybrids indicates that these two species share different forms of a basic genome (S), which accounts for the complete sterility of the hybrids. Therefore, although hybrids are produced in natural populations, the two taxa are apparently well isolated and gene flow between them looks highly improbable. The S genome is also known to be present in A. ternatus, a South American triploid with strong similarities to A. macrothrix.

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