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First evidence of sexual self defense in plants reported

Dr. Andrea Cocucci from the Instituto Multidisciplinario de Biologia Vegetal of Argentina and colleagues reported the first conclusive evidence that plants have evolved a competitive strategy and defensive structures to promote the continuation of their species in the March 20, 2014, edition of the journal New Phytologist.

This is an example of the horned pollinaria found in South American milkweed.
Credit: Andrea Cocucci Usage Restrictions: None

The conclusions were reached based on the study of a species of milkweed (Apocynaceae) found in tropical climates and the South America milkweed genus Oxypetalum in particular.

Oxypetalum has evolved to have two horn-shaped structures attached to the plants pollen sacs. The horns have been found to serve no specific biological function except to keep individual pollen sacs from clinging to birds and insects that encounter the plant. The idea is that more pollen grains can be distributed over a wider range of territory and have a higher chance for survival if the pollen grains are not clustered together on the pollinators.

"Our results suggest that neither self-propulsion nor well-developed sensory perception are required for sexual selection to take place through intrasexual struggles," said Dr. Cocucci.

This is the first documented example of plants evolving defensive and attack structures in order to be competitive with other plants and with themselves for limited opportunities to encounter pollinators and limited areas to produce the next generation of plants.