This ecosystem worldwide is already being mixed up through different channels. I would think the US regulations not to bring foreign living systems, fruits or seeds applies also to eBay. It seems eBay or the users are breaking the law.
Url changed from <a href="http://www.theatlantic.com/science/archive/2015/10/ebay-invasive-plants/408892/?single_page=true" rel="nofollow">http://www.theatlantic.com/science/archive/2015/10/ebay-inva...</a>, which points to <a href="http://phys.org/news/2015-10-invasive-blossoming.html" rel="nofollow">http://phys.org/news/2015-10-invasive-blossoming.html</a> which points to this.