Rock flower (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

DD – flower in the sense of something that flows i.e. a river, the Hudson River + Rock Hudson, US actor. I must admit that I'd so forgotten about Rock Hudson that I actually typed rock hudson into Google to see if there was any connection between the two words. I was speculating that there might be a Hudson Rock or perhaps that Sherlock Holmes occasionally referred to Mrs Hudson as his "rock".