Gnus group names

[moabi]

Hi,

I'm using Gnus to read mail from a local dovecot imap server. Some of the groups
have names like "groupname" whereas others have names like
"nnimap+localhost:groupname", and in some cases I seem to have two copies of the
same group one in each format. Why the difference?

So that I can use notmuch to search for messages, I'd like the group naming to
be consitently one or the other. However I would prefer that the
"nnimp+localhost:" be hidden as it allows me to have a narrower group buffer.
How do I configure that? The manual talks about gnus-group-line-format but
trying to describe that says it doesn't exist.

Using No GNUS 0.17

Thanks for your help

M.