After making a comment about how some answers that seem easy are a struggle to others, I saw that the same thought occurred to you, no doubt an obvious outcome I suppose, when you consider what a mixed bag we xword addicts are!
I was OK with flower for river, as with "of course" for race track, it crops up in the telegraph cryptic xwords.
Conversely, I wasted a bit of time on 20a, trying to fit the letter R for "right" - another sly one - till I turned to the wife who doesn't do cryptic clues, and she gave me the answer by seeing the last 3 words in context, then she went on to give me 15 down, again by reading the first 2 words literally, whilst I had been trying to second guess the compiler as referring slily to the letter C (country leader) as they do.
Two lessons I have learned...1. Don't try to be too clever on the cryptics. 2. LISTEN to the wife who "doesn't do cryptic stuff"!
By the way what a sad old g*t I'm getting, joining a crossword help forum!