Well, thank you for bringing this up; Decurrent is a synonym of 'running down the stem'...I found the same site I think that you read this description. Decurrent or running down the stem I think this has to do with the awls or how the leaves attach to the stem. They use wide flaps to wrap around the stem...I am still working this one out...
Edit: John, I do believe your comfrey is White comfrey. Sorry for not answering your question directly. These plants readily make seed with Russian Comfrey and the progeny will stand taller. I looked up Decurrent and wow, found stack exchange and my answer twice, within the first few inches of the search engine results. I am not that happy with the definition but I think we get the idea.
What are your plans with comfrey? Looks like you are growing this in your lawn?