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The potential for genetic assimilation of a native dandelion species, Taraxacum ceratophorum (Asteraceae), by the exotic congener T. officinale¹

Division of Biological Sciences, 105 Tucker Hall, University of Missouri, Columbia, Missouri 65211-0074 USA

Exotic plant species can threaten closely related native congeners through asymmetric hybridization and subsequent backcrossing, the process known as genetic assimilation. I explore the initial stages of this process in Taraxacum ceratophorum (Asteraceae), the native alpine dandelion, and the invasive apomict T. officinale. In central Colorado, seven T. ceratophorum populations all occur in sympatry with T. officinale. In one large population on Pennsylvania Mountain, surveys further revealed that flowering phenologies and visiting insect taxa overlap almost completely for both Taraxacum species. Together these results indicated that heterospecific pollen transfer is likely. Crossing experiments showed that T. ceratophorum is an obligate outcrosser, and interspecific hand pollinations resulted in 37.3% seed set. However, molecular analysis of the F1 offspring indicated that only 33.2% of germinating seeds were hybrids; the remainder were selfed offspring produced from a breakdown in self-incompatibility (the mentor effect). Although the mentor effect helps reduce the production of hybrids, the asymmetrical direction of hybridization creates the potential for genetic assimilation of T. ceratophorum by T. officinale.

Key Words: Asteraceae • exotic species • genetic assimilation • hybridization • Taraxacum

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