Growing History: The Philadelphia Historic Plants Constortium will link institutions, creating a network of gardens and historic plants with materials propagated from the sites themselves. Plants exchanged will serve as material for education in their shared history, in science, and conservation.
We are also engaged in the dissemination of the stories behind the plants and the landscapes they occupy.
To see who we are, see here: https://growinghistory.wordpress.com/partnering-sites-and-people/
Growing History 
I consider the plants and trees growing in and around Philadelphia to be part of an Arboretum, Arboretum Philadelphia. Plants that have been brought here and planted serve as a source for study, research, and propagation.
Dear David Hewitt, I stumbled on an amazing picture of the Henry Avenue bridge under construction via your site. Great pic and enjoyed reading about the pine trees! It is a special grove. Regards. Todd