Hi Gerspee you do not have a römer, römers have smaller feet and rounded bowls. Your piece is generally called a 'berkemeyer'. Berkemeyers started as wooden beakers with lids, carved from a 'berkemei' - the branch of a birch tree. The prunts on the stem are reminiscent of the rough bark of the wooden beakers. This is probably why the glass was named after its wooden brother. A Berkemeyer is a drinking glass with a wide, flared bowl dating from the 15th century Germany and Holland, and still made today. They have a characteristic green or yellow colour caused by iron impurities in the sand used for glass production. The thick, hollow stem is covered with prunts providing a secure grip for hands greasy from feasting, similar to the römer. They were frequently depicted in still lifes of table settings by the Dutch masters in the 17th and 18th centuries. Try searching glass makers from Germany and Holland.
Good luck hope this helps and I will keep my eye out for your mark.