I suppose this will depend on your `ls` implementation but on my LMDE (basically Debian testing) I have:

 $ man ls | grep -- '-1'
 across -x, commas -m, horizontal -x, long -l, single-column -1,
 -1 list one file per line

As well as (yes, it's the same output)

 $ ls --help | grep -- '-1'
 across -x, commas -m, horizontal -x, long -l, single-column -1,
 -1 list one file per line