Confidence: I'm as sure as I can be.
Notes: Rather difficult plants to ID to species, but there is now a very good monograph by R.V. lansdown which makes things a lot easier. From the photo one can see that the leaf bases are joined by a small strip of tissue across the stem which narrows down the choice a bit, but not much! The leaves are notoriously plastic and often not much help. Sorry not to be more positive but they're a difficult genus.