Handel Pond Lily
Picture From Ebay. There were many variations of this lamp first patented in 1902. One, two and three light versions were made. This is a single light version with the petals fully extended. The more common ones have petals that are less open. There are also versions where all the petals are of the same color (green).
More details and pictures of the Handel Pond Lily can be found in Revi's book "American Art Nouveau Glass".