Floral reorientation: the restoration of pollination accuracy after accidents

Abstract

Plants sometimes suffer mechanical injury. The nonlethal collapse of a flowering stalk, for example, can greatly reduce plant fitness if it leads to 'incorrect' floral orientation and thus reduced visitation or poor pollination. When floral orientation is important for accurate pollination, as has been suggested for bilaterally symmetrical flowers, we predict that such flowers should have developmental and/or behavioural mechanisms for restoring 'correct' orientation after accidents. We made observations and conducted experiments on 23 native and cultivated flowering plant species in Australia, South America, North America and Europe. We found that flowers with bilateral symmetry usually have the capacity to reorient after accidents, and that this is manifested through rapid bending and/or rotation of pedicels or sexual organs or slower peduncle bending. Floral reorientation restores pollination accuracy and fit with pollinators. However, experimental floral misorientation in eight species with radially symmetrical flowers showed that, with one exception, they had little capacity to reorient their flowers, in line with expectations that the orientation of radially symmetrical flowers does not substantially affect pollination accuracy. Our results suggest that quick corrective reorientation of bilaterally symmetrical flowers is adaptive, highlighting a little-studied aspect of plant-pollinator interactions and plant evolution.

Keywords: adaptive accuracy; floral orientation; flower-pollinator fit; late floral development; plant injuries; pollination; zygomorphic flowers.