The most common and most likely answer to this crossword clue is the 8 letter word JAPONICA
I've seen this crossword clue in The Times
J
A
P
O
N
I
C
A
More clues leading to the result JAPONICA
Buddy explains!
The straight part
We know that "rosaceous shrub" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rosaceous shrub = japonica.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.
What does JAPONICA mean?
JAPONICA noun- Any of several plants originally native to Japan.