The most common and most likely answer to this crossword clue is the 8 letter word ACANTHUS
I've seen this crossword clue in The Daily Telegraph
A
C
A
N
T
H
U
S
More clues leading to the result ACANTHUS
- Chant USA when rallying for Bush
- Shrub head of arboretum is able so to provide
- Kind of leaves a prison in this way
- Heading away from empty hotel with American plant
- Shrub like this needs a container at first
- Plant in a container in the manner indicated
- Prickly plant in a container like this
- A bog therefore will supply decorative plant
- Bloomer having a toilet wrongly shut
- Vessel like this supporting a plant
Buddy explains!

The straight part
We know that "prickly plant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case prickly plant = acanthus.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 ACANTHUS mean?
ACANTHUS noun- A member of the genus Acanthus of herbaceous prickly plants with toothed leaves, (family Acanthaceae, order Scrophulariales) found in the south of Europe, Asia Minor, and India.