Carol rewrote sentence to reveal algae (9)

I believe the answer is:

coralline

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

'algae' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?

'carol rewrote sentence' is the wordplay.
'rewrote' is an anagram indicator (I've seen 'rewritten' mean this).
'sentence' becomes 'line' (I am not sure about this - if you are sure you should believe this answer much more).
'carol' is an anagram of 'coral'.
'coral'+'line'='CORALLINE'

'to reveal' acts as a link.

Can you help me to learn more?

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app