Posted: 16/12/2013 at 13:23
It's usually the stems of Japanese knotweed that are used in floral arrangements. Sometimes dried but also fresh stems. http://blog.pottingsheduk.com/?paged=3 (scroll down to "Mysterious Aroid")
Carol, if the arrangements have fresh stems in them, please be careful when disposing of the stems and make sure they can't get composted.