In order to increase the amount of pollen they disperse, several varieties of mistletoe have developed “spring-loaded” flowers that burst open, showering pollen on visiting pollinators.
These spring-loaded flowers generate tension as stored mechanical energy. Tension is generated within the flower as the inner stamen (a reproductive organ containing pollen) and outer petals of the flower grow at different rates. This differential growth causes the flowers to bulge out until the petals eventually split from each other. This creates small openings between the petals, allowing the flower to bulge out further, which further increases tension. When the flowers are mature, mechanical disturbance from pollinators will trigger opening of the petals. The stamens first spring up vertically, then the anthers (which are located on the top of the stamen and contain pollen), move out horizontally, catapulting pollen grains up into the air and onto the pollinator.
Mistletoe flowers can be opened in two different ways. Birds can “unzip” the petals at their base, triggering flower opening and showering the birds in pollen. Birds can also grasp and pull the petals, also resulting in flower opening and pollen dispersal. The explosion of pollen catapults the pollen grains straight up and away from the flower’s center. Unsuspecting pollinators are blanketed in pollen and help to cross-pollinate other mistletoe plants as they move between flowers. Residual pollen grains that don’t land on the bird are still hurled high enough into the air (up to 20 centimeters) to allow for the grains to also be dispersed by the wind.
This strategy was contributed by Christy Cael and Carol Gustafson.Edit Summary
“Some African genera such as Erianthemum, Actinanthella, and Oedina are highly specialized for bird-pollination. Their flowers change color at maturation, and their tubular corollas split along the petal junctions to form window-like fenestrae. This fenestration results from tension generated by differential growth of the stamens, which are fused to the petals below the fenestrae but free above (Kirkup, 1998). The pollinating sunbirds insert their beaks through the fenestrae, thus triggering rapid flower opening, inward coiling of the filaments, and deposition of pollen on the bird’s head.” (Vidal-Russell and Nickrent 2008:1027).
Evolutionary relationships in the showy mistletoe family (Loranthaceae).Am. J. Bot. 9(8): 1015-1029.August 1, 2008
“Another species in the same family [of tropical mistletoe] stores its pollen in the roof of its flower. As a bird lands, its weight triggers the chamber so that it opens explosively and showers pollen all over the bird’s forehead.” (Attenborough 1995:117)