The most common and most likely answer to this crossword clue is the 8 letter word COWSLIPS
I've seen this crossword clue in The Times
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Buddy explains!

The straight part
We know that "flowering plants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flowering plants = cowslips.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 COWSLIPS mean?
COWSLIPS noun- A low-growing plant, Primula veris, with yellow flowers.
- Any of several other plants related or similar in appearance
- Short for cowslip tea: a kind of green tea; an herbal tea made with cowslip flowers.