You have to be invited to view discussions. A Study Group can be a serious effort towards acquiring genuine knowledge on the subject or just a pastime in which a lot of random people just post whatever they are in the mood to. Certain groups of plants can be very difficult, like Hippeastrums, and one hopes some advance takes place and of course this is what maintains the Group alive. Hence the selection of people. Yes, they are open but to anyone invited to join.