The most common and most likely answer to this crossword clue is the 10 letter word FIDDLEHEAD
F
I
D
D
L
E
H
E
A
D
More clues leading to the result FIDDLEHEAD
Buddy explains!

The straight part
We know that "tall fern" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tall fern = fiddlehead.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 FIDDLEHEAD mean?
FIDDLEHEAD noun- The scroll-shaped decoration at the tip of a fiddle.
- A similar scroll-shaped ornament on a ship's bow.
- The furled fronds of a young fern harvested for food consumption.