The biomechanics of Cornus canadensis stamens are ideal for catapulting pollen vertically

Abstract

Summary1. Rapid movements in fungi and plants have evolved in different species to facilitate the dispersal of spores and seeds. The mechanisms of action can differ among species, but the effectiveness of these movements has rarely, if ever, been tested. Here we show through a quantitative biomechanical analysis that the stamens of Cornus canadensis L. (bunchberry) are ideal for catapulting pollen vertically at high speeds. 2. We develop a biomechanical model to describe the explosive launch of pollen from the flowers of bunchberry. The model determines the equation of motion for the stamens based only on the morphology and measurements of the parts of the stamens. To measure the motion of the stamens to compare with our model, we analysed individual frames of a video taken at 10 000 fps. 3. The thecae of adjacent stamens dehisce in bud so that the stomia face each other, retaining pollen between neighbouring anthers. As the flowers open, pollen is accelerated vertically as long as the thecae remain in contact. Pollen is released only when the anthers move horizontally and separate. 4. The observed motion of the stamens matches the results from our model through release of the pollen. The model reveals that pollen release (horizontal movement of the anthers) occurs only after the vertical speed is at its maximum. Thus, for this particular catapult mechanism, the morphology of the stamens is optimal for launching light, dry pollen straight upwards at high speed. Pollen launched vertically at high speed both enhances insect pollination by helping to making pollen stick on visiting insects, and also allows for successful wind pollination by propelling pollen into the air column. Seed set by inflorescences in pollinator-exclosure cages further supports the ability of this flower to use wind as a pollination mechanism.

Functional modularity in a forcible flower mechanism: relationships among morphology, biomechanical features and fitness

“…However, all these studies detected functional modules by exploring the correlations of morphometric variables, without including biomechanical traits. In addition, although other studies have considered biomechanical aspects of flower mechanisms (Brantjes 1981a, b;Brantjes and De Vos 1981;Cocucci 1989;Sérsic 1991;Whitaker et al 2007;Sprayberry and Suver 2011;Muchhala and Thomson 2009), only a few (Brantjes 1981a, b;Claßen-Bockhoff et al 2004;Reith et al 2007;Córdoba and Cocucci 2011) have quantified the force needed to operate a floral mechanism. In the case of keel flowers, it was possible to correlate the force necessary to open the keel with morphometric variables to detect the group of floral traits that constitute a functional module (see Córdoba and Cocucci 2011).…”

Ingenious floral structure drives explosive pollination in Hydrilla verticillata (Hydrocharitaceae)

“…; Whitaker et al . ). No matter what mechanism is adopted to release pollen, many explosive pollination processes recorded in previous articles occur on the mother plant, but not all of them.…”

“…; Whitaker et al . ; Wong Sato & Kato ). Many special structures and mechanisms have evolved in different species to make stamens move at high speeds and release pollen explosively.…”

Pressure-actuated cellular structures

“…This leads to an initially vertical acceleration of the anthers that start to rotate after the separation from the inset. The rotational velocity of the anther increases its vertical tip velocity so that the pollens are accelerated to speeds of up to 7.5 m/s [314]. Pollens that weight about 24 µg are dispersed by this mechanism to altitudes of 25 mm.…”