The most common and most likely answer to this crossword clue is the 9 letter word CORCHORUS
C
O
R
C
H
O
R
U
S
Buddy explains!
The straight part
We know that "fibre-producing plants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fibre-producing plants = corchorus.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.