Crossword Genius

Thorny plant becomes coated, they say (5)

Ross

I believe the answer is:

furze

I'm a little stuck... Click here to teach me more about this clue!

This clue might be a double definition.

'thorny plant' is the first definition.
The answer and definition can be both plants as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'coated they say' is the second definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'becomes' is the link.

Can you help me to learn more?

(Other definitions for furze that I've seen before include "Dreamlike" , "Bushy growth" , "Spiny shrub" , "Another word for gorse" , "one shrub" .)

I've seen this clue in The Guardian.
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