Cryptic crossword clue
Extremely arrogant, uprooting unknown plant 7

The most common and most likely answer to this crossword clue is the 7 letter word VERVAIN

I've seen this crossword clue in The Guardian
V
E
R
V
A
I
N

Buddy explains!

The straight part
We know that "plant/plant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plant/plant = vervain.
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 VERVAIN mean?

VERVAIN noun
  1. A herbaceous plant, Verbena officinalis, common in Europe and formerly held to have medicinal properties.

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