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22-Jul-2010

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How exploding moss launches its spores



Habit shot of the low-growing Sphagnum moss showing reproductive heads with capsules raised above the mat by pseudopodia. Some capsules are round and not yet exploded, and some have recently exploded (cylindrical).
Image courtesy of Joan Edwards

When Sphagnum moss spores explode out of their capsules, they reach more than 10 centimeters in the air, thanks to tiny mushroom clouds that help drive the spores upward, scientists have found.

The same sort of fluid spirals also help propel jellyfish and squid through water, but these so-called "vortex rings" haven't generally been associated with plants, until now.



Three capsules from Sphagnum henryeuse. Two are round (unexploded) and one that has already exploded.
Image courtesy of Joan Edwards

Sphagnum moss forms thick mats covering approximately 1 percent of Earth's land surface and is important in the global carbon cycle, potentially storing more carbon than any other plant genus. To reproduce, the ground-hugging moss must launch its spores high enough to be picked up by wind and carried long distances.

In a study appearing in the 23 July issue of the journal Science, Dwight Whitaker of Pomona College and Joan Edwards of Williams College show that the spores reach heights that cannot be explained simply by the force that initially blasts them out of their capsules.

By capturing high-speed video of the spores launched from exploding capsules, the researchers discovered that vortex rings provide the additional boost that carries the spores high enough to be dispersed by wind.

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