Pictured above is the Coastal Sandbur more commonly called 'sand spur' (Cenchrus spinifex Cav.), a ubiquitous and very annoying resident of our sandhill. The main barbs have reverse spikes that imbed in clothes and flesh alike.
These grasses are sharply barbed and easily hitch a ride on anyone or anything that passes including car tires.
October 14, 2008
Observatory
The New York Times
Plant Seeds Hitch Rides on Traveling Shoes
We are all accidental Johnny Appleseeds. Along with wind, water and animals, people can spread seeds around. They get picked up by shoes or car tires, for example, and end up elsewhere.
“But we’ve never looked at quantifying it, at how many seeds get transported over what distances,” said Matthias C. Wichmann, of the Center for Ecology and Hydrology at Wallingford in England.
Dr. Wichmann and a team of researchers have now done that, and their findings are surprising: seeds can hitch a ride on shoes for miles.
In the study, in The Proceedings of the Royal Society B: Biological Sciences, the researchers looked at two wild plants that are found in a narrow band along a cliffside path in southern England that is frequented by millions of day hikers annually. The researchers wondered if all that walking contributed to the spread of the plants.
So they devised laboratory experiments in which people wearing hiking shoes or rubber boots stepped in mud, then in a tray containing a specific number of seeds, and then walked a given distance, from one meter (3 feet 3 inches) to five kilometers (a little over three miles). Seeds remaining on the shoes were then counted.
They found that, as might be expected, most of the seeds fell off during the first 10 to 20 meters. But even with walks of five kilometers, a few seeds remained. Computer simulations showed that dispersal by shoes was more important over long distances than dispersal by wind, which with these seeds is generally limited to about 250 meters.
Dr. Wichmann said that while such long-distance dispersal by walking might be rare, it might have a profound effect on the spread of certain species, particularly invasive ones that are new to a region. “Only a few seeds may go very far,” he said. “But these are the pioneers — they colonize new sites.”
A close-up of the Coastal Sandbur from the USDA plant files, below.
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