Flower orientation enhances pollen transfer in bilaterally symmetrical flowers

Atushi Ushimaru, Ikumi Dohzono, Yasuoki Takami, Fujio Hyodo

Research output: Contribution to journalArticlepeer-review

57 Citations (Scopus)


Zygomorphic flowers are usually more complex than actinomorphic flowers and are more likely to be visited by specialized pollinators. Complex zygomorphic flowers tend to be oriented horizontally. It is hypothesized that a horizontal flower orientation ensures effective pollen transfer by facilitating pollinator recognition (the recognition-facilitation hypothesis) and/or pollinator landing (the landing-control hypothesis). To examine these two hypotheses, we altered the angle of Commelina communis flowers and examined the efficiency of pollen transfer, as well as the behavior of their visitors. We exposed unmanipulated (horizontal-), upward-, and downward-facing flowers to syrphid flies (mostly Episyrphus balteatus), which are natural visitors to C. communis. The frequency of pollinator approaches and landings, as well as the amount of pollen deposited by E. balteatus, decreased for the downward-facing flowers, supporting both hypotheses. The upward-facing flowers received the same numbers of approaches and landings as the unmanipulated flowers, but experienced more illegitimate landings. In addition, the visitors failed to touch the stigmas or anthers on the upward-facing flowers, leading to reduced pollen export and receipt, and supporting the landing-control hypothesis. Collectively, our data suggested that the horizontal orientation of zygomorphic flowers enhances pollen transfer by both facilitating pollinator recognition and controlling pollinator landing position. These findings suggest that zygomorphic flowers which deviate from a horizontal orientation may have lower fitness because of decreased pollen transfer.

Original languageEnglish
Pages (from-to)667-674
Number of pages8
Issue number4
Publication statusPublished - Jul 2009
Externally publishedYes


  • Commelina communis
  • Flower orientation
  • Horizontal
  • Pollinator specialization
  • Zygomorphic flower

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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