Spring-loaded Flowers Ensure Pollen Dispersal

photograph of red and yellow flowers on a tree

Biological Strategy

Sandalwood family

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Disperse Seeds

Plants disperse their seeds using a variety of mechanisms, including wind, rain, and attachment to animals. Seed dispersal can be important if plants growing too close together will compete for resources, such as nutrients and sunlight. Since plants are literally rooted in place, seed dispersal is also an important mechanism for expanding their range or reaching new environments.

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Pollinate

One of the ways that plants can produce offspring is by making seeds that contain the genetic information to produce a new plant. Seeds can only be produced when pollen grains reach the hidden ovaries within a flower. Flowers have developed wildly diverse forms and activities, such as the production of sweet nectar to attract organisms such as bees and butterflies, that move from flower to flower, transferring pollen. Flowers will also adapt to make use of environmental influences such as wind and water as pollinators.

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Sense Touch and Mechanical Forces in a Living System

Perceiving touch enables living systems to detect other living systems around them and environmental conditions, such as air movement, water currents, and temperature. This ability can help them sense danger as well as opportunity, as when a Venus flytrap’s hairs sense the presence of an insect to eat. Sometimes, a living system senses touch or mechanical forces at a coarse scale; other times, at a sensitive scale that detects very subtle differences. For example, a human elbow is not nearly as sensitive to textures as human fingertips. Fingertips have dermal ridges and many nerve endings that increase sensitivity, enabling them to explore the environment in detailed ways. Elbows don’t need to sense at that level of detail.

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Transform Mechanical Energy

Mechanical energy is made up of kinetic energy (the energy of an object in motion) and potential energy (stored energy). Organisms use mechanical energy in a variety of ways, including capturing prey, transporting seeds, and moving around.

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Expel Solids

Living systems must often discharge solids–such as seeds, eggs, pollen, and mineral salts–for reproduction, protection, or other reasons. Solids can be easily moved when a living system applies force to them. But creating that force requires energy, so living systems must either have efficient strategies worth the energy investment or use an outside force (such as gravity). For example, a tropical mistletoe positions its pollen so that the weight of a bird landing nearby triggers the pollen’s release onto the bird’s forehead. The bird then fertilizes other mistletoes that it visits.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Flowers of the mistletoe use stored mechanical energy to release pollen.

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.

Last Updated July 21, 2017

References

“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).

Journal article

Evolutionary relationships in the showy mistletoe family (Loranthaceae).

Am. J. Bot. 9(8): 1015-1029. | 01/08/2008 | Vidal-Russell R, Nickrent DL.

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Reference

“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)

Book

The Private Life of Plants

21/08/1995 | David Attenborough

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Reference

Journal article

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

Functional Ecology 21(2): 219-225. | 07/02/2007 | Whitaker DL, Webster LA, Edwards J

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Reference

Journal article

Explosive flowering, nectar production, breeding systems, and pollinators of New Zealand mistletoes (Loranthaceae).

New Zealand Journal of Botany. 35(3): 345-360. | 01/05/1997 | Ladley JJ, Kelly D, Robertson AW

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