The most common and most likely answer to this crossword clue is the 6 plus 5 letter word RAGGED ROBIN
I've seen this crossword clue in The Times
R
A
G
G
E
D
R
O
B
I
N
More clues leading to the result RAGGED ROBIN
Buddy explains!

The straight part
We know that "Perennial" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case perennial = ragged robin.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.