When scientists at the Institute for Ecology at Berlin's Technical University began investigating patterns of plant-life mobility, they found out that seeds are hitching rides on car tires and bumpers and crossing thousands of kilometers.

The result is clearly visible along Germany's dual carriageways, now resplendent with shiny red bell peppers and luscious tomatoes which nestle happily among some decidedly unusual herbs such as lambsquarters and scurvy grass -- more commonly found along coastlines.

"Half of the 11,000 seedlings we identified were not native to German soil," project leader Moritz von der Lippe told Spiegel Online.

Seedy souvenirs

Obviously, holiday-makers are bringing home a few more souvenirs from their travels than they realize.

Germany's barren motorways landscapes might seem like an unlikely setting for plants used to sumptuous salty soil, but apparently, they're ideal.

"The grit along the roads creates perfect conditions for coastal wildlife," von der Lippe said.

Illegal immigrants

Before you start calculating how much money you can save by trading in the organic supermarket for the freeway, bear in mind that this herbaceous invasion isn't all good news.

"It's driving out the indigenous plant-life," von der Lippe said. Goldenrod from North America is one particularly aggressive import that's been terrorizing the weedy European flora and fauna for years.

"Seed-trafficking is the most serious ecological problem of our times," proclaimed the Neue Züricher Zeitung recently.