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Keywords:

  • Aristolochia;
  • biomechanics;
  • crystalline wax;
  • flower biology;
  • force measurements;
  • pitfall flower;
  • trapping trichome

Summary

  • Catching insects to ensure pollination is one of the most elaborate and specialized mechanisms of insect–plant interactions. Phylogenetically, Aristolochiaceae represent the first angiosperm lineage that developed trap flowers. Here we report the structure and function of specific trichomes contributing to the highly specialized trapping devices.
  • Investigations were carried out on six Mediterranean Aristolochia species. The morphology and arrangement of the trapping trichomes were investigated by scanning electron microscopy (SEM) and cryo-SEM. To demonstrate frictional anisotropy of the trapping trichome array, a microtribological approach was used.
  • The results of our experiments support a hypothesis long proposed, but never tested, regarding the trapping mechanism in proterogynous Aristolochia flowers: that an array of highly specialized trichomes arranged eccentrically to the underlying surface is responsible for the easy entrance of insects into flowers but impedes their escape. As they enter the male stage of anthesis, flowers significantly modify their inner surface characteristics, allowing insects to leave.
  • We have demonstrated the substantial contribution of trapping trichomes to the capture, retention and release of pollinators, an important prerequisite for making cross-pollination possible in most Aristolochia species. Finally, we compare trapping trichomes of Aristolochia with similar structures found in other trapping flowers as well as in pitchers of carnivorous plants not optimized for insect release.