The most common and most likely answer to this crossword clue is the 9 letter word PEDIGREES
I've seen this crossword clue in Financial Times
P
E
D
I
G
R
E
E
S
Buddy explains!

The straight part
We know that "Lines" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lines = pedigrees.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 PEDIGREES mean?
PEDIGREES noun- A chart, list, or record of ancestors, to show breeding, especially distinguished breeding.
- A person's ancestral history; ancestry, lineage.
- Good breeding or ancestry.
- The history or provenance of an idea, custom etc.
- The ancestry of a domesticated animal, especially a dog or horse.