The most common and most likely answer to this crossword clue is the 6 letter word OXALIS
I've seen this crossword clue in The Guardian
O
X
A
L
I
S
More clues leading to the result OXALIS
- Farm animal ails after chewing wood-sorrel
- Round 10: greatest boxer first to succumb in plant
- Plant kiss on round lips, softly going to hug one
- One of the sorrels is following ring, reverse of slack
- Ring teams to corral a large sorrel
- Animal to sail off with plant
- Tesco ultimately wrong: supermarket out of Germany succeeded —
- Measurement system not strict over regressing 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 = oxalis.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 OXALIS mean?
OXALIS noun- Any of various ornamental flowering plants of the genus Oxalis