The most common and most likely answer to this crossword clue is the 9 letter word HOLLYHOCK
I've seen this crossword clue in The Daily Telegraph
H
O
L
L
Y
H
O
C
K
More clues leading to the result HOLLYHOCK
Buddy explains!
The straight part
We know that "Plant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plant = hollyhock.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 HOLLYHOCK mean?
HOLLYHOCK noun- Any of several flowering plants of the genus Alcea in the Malvaceae family.