The New Frontier of Plant Violence

Barbed pollen sacs are "weapons"

Milkweed might be more violent than you'd expect.     Photo: Getty Images/iStockphoto

Plants have always been harbingers of peace in our violent world. From towering redwoods to peaceful begonias, flora tends to be far more tranquil than fauna. But this characterization might be inaccurate, if we're to believe new research published in the journal New Phytologist.

Male animals famously fight over mates, but now scientists have discovered similar mechanisms in some male plants. It might sound like science fiction, but when botanists studied the South American milkweed, they discovered the species had evolved "weaponry" to improve its chances of passing on its genes.

If you know anything about plant physiology and reproduction, you're probably shaking your head. "Male animals duke it out for superiority, but plants are quite literally rooted to where they stand," you may think. "What gives?"

The answer is fairly subtle. Milkweed, like many other plants, reproduces by hooking pollinia—sacs of pollen grains—to the bodies of pollinators, such as birds. These animals move about to other plants, distributing the pollinia and completing the fertilization process.

Sometimes pollinators pick up multiple pollinia, and that's where the violence comes in. Researchers discovered horn-like structures on the plants that appear to serve no biological purpose besides preventing pollinators from acquiring other pollen sacs that would otherwise hook on to one another. The horns assert the dominance of the male plant whose pollinia is picked up first by a pollinator.

A mating fight between bears or lions may be far more dangerous—but this new research proves violence may be truly universal.

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