Reorientation of daffodil (Narcissus : Amaryllidaceae) flowers in wind: Drag reduction and torsional flexibility

Daffodil Bowers extend laterally from the long axes of their stems; as a result, wind on a Bower exerts torsional as well as flexural stress on the stem. Stems respond by twisting, and thus Bowers reorient to face downwind in moderate winds, in the process reducing their drag by similar to 30%. This repositioning is facilitated by the stems' relatively low torsional stiffness. Daffodil stems have a ratio of flexural to torsional stiffness of 13.27 +/- 0.96 (SD), compared with 8.33 +/- 3.20 (SD) for tulip stems, which bear flowers as symmetrical extensions of their long axes, and compared with 1.5 for isotropic, incompressible, circular cylinders.