Mean to confine flower that's fibrous (7)
The confirmed answer is
I can see the definition, and I think part of the wordplay, but not all of it. Here's my understanding:
fibrous = def
mean (to) = TRY
flower = some river, presumably ING
So we have TRY confine ING = TRINGY.
But where does the first letter come from? (Or maybe I should phrase it this way: how does it get into first position?)