Scientists have warned that online auction platforms such as EBay are fueling the spread of invasive plants across the globe.

The plants Goldenrod, Himalayan balsam, Chinese windmill palm are not native to Europe, but all have been introduced into Switzerland as houseplants and "escaped" into the wild, ETH Zurich reported. Phenomena such as this has been observed on every inhabited continent.

To estimate how much of the dangerous spread of invasive species was a result of online trading, a team of researchers took on the task of monitoring the online trade of about two thirds of the world's flora on eBay and nine other online trading platforms for a period of 50 days. The team tracked which plant species were put up for sale or auctioned in different countries and how often they were posted using a newly-developed software program. The computer program was only able to look at plant sales from the supply side of things, but was still able to gather valuable information on the plant trade.

Over the course of the study, the researchers pinpointed 2,625 different plant species offered for sale on eBay, 510 of which are already considered invasive in some part of the world and 35 that are on the IUCN's list of the 100 worst invasive species. The researchers found Passiflora edulis (passionfruit) is the invasive plant most frequently put up for sale on these sites. It appears about 90 times per day and was spotted being offered in 17 countries across five major geographic regions. This species is believed to be highly invasive in the tropics. The second most frequently offered plant proved to be the cornflower Centaurea cyanus, which is considered invasive in certain parts of the United States and was offered in 10 countries in five regions. People were observed to sell plants in 65 countries, and 55 of these countries ihad offered endangered plants.

"That was unexpected, since the Australians don't allow you to bring any invasive plants across their borders. But surprisingly, there are apparently no controls in place to make sure potentially harmful plants don't leave the continent," said Christoph Kueffer, senior lecturer at the Institute of Integrative Biology.

The study highlights how invasive plant species can be easily purchased with the "click of a mouse." It also demonstrates that these rarely policed transactions could be monitored.

"As online trade blossoms, it makes it even more urgent for the authorities to take action or for responsible large commercial nurseries to adjust their product ranges," Kueffer concluded.

The findings were published in a recent edition of the jorunal Conservation Biology.