Food / Herb used in Polish rosol (chicken soup)? [88]

My grandmother makes rosol which is a favorite of mine but she uses a herb that she grows in her garden. She calls it 'maggie' but doesn't really know the real name of it. It has a bit of a celery smell to it but it is not celeriac. It is smaller. Does anyone know the name of it?? I'm desperate to find it. It gives the soup such an amazing flavor.