Task: Sentence Expansion
Input (English): The southern beeches Nothofagus previously thought closely related to beeches , are now treated as members of a separate family , Nothofagaceae .
Output (English): The southern beeches ( genus " Nothofagus " ) previously thought closely related to beeches , are now treated as members of a separate family , the Nothofagaceae ( which remains a member of the order Fagales ) .