The most common and most likely answer to this crossword clue is the 7 letter word BULRUSH
I've seen this crossword clue in The Guardian
B
U
L
R
U
S
H
More clues leading to the result BULRUSH
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 = bulrush.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 BULRUSH mean?
BULRUSH noun- Any of several wetland plants, mostly in the family Cyperaceae (the sedges):