I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
That stem is most likely a fasciated shoot which happens to various types of plants from time to time. I am not sure how much luck you will have propagating it. However, the following web sites are excellent guides for the details of how to propagate shrubs including roses. They will provide much more detail than we can in this short space: http://muextension.missouri.edu/xplor/agguides/hort/g06970.h...
Thanks for the question. Please stop in again soon!
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