Ginkgo biloba tree at the Smithsonian Castle
Two ginkgos flank the south entrance to the 1855 Smithsonian Castle, the oldest building at the Smithsonian. The trees were planted in 1986 as part of the 4.2-acre Enid A. Haupt Garden, which serves as a living “rooftop” for three underground Smithsonian buildings: the National Museum of African Art, the Arthur M. Sackler Gallery, and the S. Dillon Ripley Center.

More information can be found in the book "A New View from the Castle" by Edward Park and J.P. Carlhian.
Photo by Darren Milligan, used under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 Generic license.