the Polish site also mentions Janina as a newer version of Joanna.
I think they're probably all variants of the female version of John which has these names as female versions:
Joan, Joanna, Joanne, Joann, Jan, Jane, Jayne, Jayna, Janet, Janice, Janis, Jean, Jeane, Jeanne, Jeannie
this is the bit you tel me we are related.
On PF anything is possible ;)