The most common and most likely answer to this crossword clue is the 7 letter word LOBELIA
I've seen this crossword clue in The Times
L
O
B
E
L
I
A
More clues leading to the result LOBELIA
- One in bed with a bit of ear and back trouble
- Book marks found in city plant
- I’ll go up to receive award and a blue-flowering plant
- Division of leaf on large heart of speciality plant
- Bloomer liable to crumple without oxygen
- Projecting part, large one attached to a plant
- Garden flower, look, the devil when cut finally
- Direction signs installed in Louisiana plant
- Plant old bishop and priest put in US city
- Lamb follows to toss plant
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 = lobelia.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 LOBELIA mean?
LOBELIA noun- A member of the genus Lobelia, flowering plants in the Lobelioideae subfamily pf family Campanulaceae, containing many species, some of which are garden plants.