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Sunflower Helianthus anomalus
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Sunflower (Helianthus anomalus).

May 7, 2010
Sunflower (Helianthus anomalus).

More About this Image: To try and determine how much of a role chance plays in evolution, National Science Foundation (NSF)-supported evolutionary biologist Loren Rieseberg and his colleagues at Indiana University conducted experiments using the anomalous sunflower, or Helianthus anomalus, a naturally-occurring hybrid. The anomalous sunflower was the result of interbreeding two other sunflowers: the common sunflower (Helianthus annuus) and the petioled sunflower (Helianthus petiolaris). Rieseberg and his team assumed they could interbreed the two parent species and get another flower but did not know if they would still get the anomalous sunflower or if a totally new species would develop after a few generations.

In the three trials they conducted, the anomalous sunflower reappeared within four generations. Additionally, not only did the flowers look like their counterparts found in the Great Basin desert, DNA testing showed that they were almost identical. The outcome was a surprising finding since much of evolutionary theory suggests that chance is a significant player in speciation.


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