The most common and most likely answer to this crossword clue is the 10 letter word POINSETTIA
I've seen this crossword clue in The Times
P
O
I
N
S
E
T
T
I
A
More clues leading to the result POINSETTIA
- Petitions a foreign plant
- Moved into a site east of power plant
- Small picture in vessel, one next to a shrub
- Plant opiate isn’t distributed
- House plant‘s site? In a pot, strangely!
- A petition’s developed in plant
- . Curiously, opiate isn’t something you find in pot
- Plant put in place before I initially arrived
- Bloomer associated with Xmas in Thailand misbehaving with opiates
- Shrub planted in location one approved initially
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 = poinsettia.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 POINSETTIA mean?
POINSETTIA noun- A plant, Euphorbia pulcherrima, with rather small and insignificant flowers but large brightly coloured leaves.