Most often, you do not need to have an official title to take a leadership position. I have seen many circumstances where the titled leader would actually follow the informal leader that was put in place by the group. In some circumstances though, it does help the leader if they also have the title so that they are recognized by peers and superiors for they title as it pertains to communication and development within the organization. And so that the leader can continue to work for the benefit of his subordinates when speaking with his/her superiors.