What does the cryptic crossword clue "Series about fungus, not really to catch fire (8)" mean?

The wordplay uses a container (one word inside another). MOULD (synonym="fungus") in SER (synonym="series") = SMOULDER The answer is SMOULDER.

Series about fungus, not really to catch fire (8)

Guardian Cryptic #29483 | 22 Across | 2024-09-09 flower